The best place to start when choosing a welding machine is with the work you expect it to do: the material, its thickness, your workload and the power supply available. Once you have those details, it becomes much easier to compare machines and find one that can handle your usual jobs without unnecessary expense or frequent cooling breaks.
This guide explains how amperage, duty cycle and power supply fit together, then uses them to help you narrow down the options. It also clears up two figures that can be confusing when comparing specifications: how long a machine can weld at a given output, and how much current it needs from the mains.
👉 Browse MIG welders, TIG welders, MMA welders, multi-process machines and spot welders, or ask our team what suits your work.
In this guide:
Understanding Amperage and Duty Cycle
Understanding Welding Current
Welding current is one of the main factors affecting heat at the joint, alongside voltage, travel speed and the process itself. For mild steel MIG welding, about one amp per 0.001 inch of thickness, or roughly 40 amps per millimetre, is a useful starting estimate. That puts 3 mm steel at around 120 amps, but the joint design, wire, gas and number of passes still determine the settings you need.
The material also affects how heat moves through the joint. Stainless steel retains heat more readily than mild steel, so it often needs less current for comparable work. Aluminium conducts heat away quickly and can need considerably more. Use settings for the specific material and process rather than applying a fixed percentage adjustment.
Allow some capacity above the work you do most often. If 6 mm steel is a regular job, for example, it is worth comparing a 250 amp machine with a 200 amp model. The larger machine may sustain your working current for longer, but check the duty-cycle ratings: maximum amperage alone does not tell you which will cope better.
Matching Duty Cycle to Your Workload
Duty cycle tells you how much of a ten-minute period an arc welder can operate at a stated current under its rated conditions. A rating of “200 A at 40%” allows four minutes of welding at 200 amps followed by six minutes of cooling. At a lower current, the machine will usually be able to weld for longer, so look for the rating at the output you expect to use.
- A lower current usually allows a longer duty cycle. A higher-output machine may therefore be useful even when you rarely use its maximum setting. Check its published continuous-output rating rather than assuming what it will sustain.
- Check the temperature used for the rating. EN 60974-1 duty-cycle ratings normally use a 40°C ambient temperature. Conditions above the rated temperature, direct sunlight or restricted cooling can reduce the available welding time.
- Allow for the pauses built into your work. Repositioning parts, tacking, cleaning and checking welds all reduce arc-on time. A lower duty cycle may suit these jobs, while long production runs need more continuous capacity.
- A thermal cut-out protects the machine from overheating. Let it cool as instructed if the warning appears. Repeated trips call for a check of the workload, ventilation and cooling system, rather than simply accepting them as normal.
| Use case | Duty cycle to look for | Typical work |
|---|---|---|
| Hobby and occasional repair | Around 20 to 40% may suit intermittent work; check the rating at your working current. | Bodywork, garden gates and light fabrication with pauses between welds. |
| Light and general fabrication | Around 40 to 60% can be useful where runs are longer; compare at the current you need. | Brackets, frames, trailers and general repairs. |
| Production and heavy fabrication | Often 60% or higher at the working current, with 100% where continuous welding is required. | Structural work, repeat production and long welding runs. |
Welding Machine Comparison at a Glance
| Process | Weld quality | Speed | Ease of use | Machine cost | Best for |
|---|---|---|---|---|---|
| MIG (GMAW) | Clean welds with the right setup. | Fast. | Relatively easy to learn. | Mid-range. | Bodywork and general steel or aluminium fabrication. |
| TIG (GTAW) | Precise control and a neat finish. | Usually slower. | Needs more coordination and practice. | Often higher, especially AC/DC. | Thin material, stainless steel, aluminium, specialist alloys and pipework. |
| MMA / Stick (SMAW) | Sound welds with suitable electrodes; slag needs removal. | Moderate, with stops for electrodes and cleaning. | Simple equipment; arc control takes practice. | Often a lower initial cost. | Outdoor repairs, site work and thicker sections with prepared joints. |
| Flux-cored (FCAW) | Sound welds with the right setup; slag needs removal. | High deposition on suitable work. | Similar wire-feed technique to MIG. | Depends on the system. | Heavy fabrication. Self-shielded wires suit outdoor work; gas-shielded wires need wind protection. |
| Multi-process | Depends on the selected process. | Depends on the process. | Each process still needs its own skills. | Mid-range to higher. | Workshops needing several processes from one power source. |
| Spot welding (RSW) | Repeatable sheet joints after setup and testing. | Very fast per joint. | Straightforward after setup. | Depends on capacity. | Sheet-metal production and suitable vehicle-panel repairs. |
- MIG is a useful first choice for general steel fabrication, particularly when you want straightforward setup and good productivity on a range of workshop jobs.
- TIG suits work where precise control and appearance matter, including thin stainless steel and aluminium. It takes more practice and is usually slower than MIG.
- MMA is well suited to outdoor and site work, especially where carrying a shielding-gas cylinder is inconvenient. It still needs proper joint preparation, including removal of unsuitable coatings and contamination.
- Consider a multi-process machine if your work varies. Many combine MIG, MMA and DC TIG, but check the actual modes and accessories included, particularly if you want AC TIG for aluminium.
Amperage vs Material Thickness
| Thickness | Mild steel MIG: example current | Notes |
|---|---|---|
| 1 mm | 30 to 50 A | A broad MIG starting range with 0.6 to 0.8 mm wire and short-circuit transfer. Control heat carefully to avoid burn-through. |
| 2 mm | 60 to 90 A | Often paired with 0.8 mm wire for light sheet work; adjust to the joint and welding guide. |
| 3 mm | 90 to 130 A | A starting range for lighter fabrication, often with 0.8 mm wire. Check that the settings provide adequate fusion. |
| 6 mm | 170 to 220 A | Choose wire and gas for the intended settings. Butt joints may need bevelled edges and several passes. |
| 10 mm | 250 to 300 A for higher deposition | An example range for productive MIG work with suitable wire, gas and preparation. Multi-pass procedures can also use lower currents. |
| 12 mm and over | 300 A or more for higher deposition | A machine-sizing example, not a minimum current for every pass. Joint preparation and a suitable multi-pass procedure determine the actual settings. |
The figures above are broad starting ranges for mild steel MIG welding, with joint preparation and multiple passes where needed. Use separate settings for TIG and MMA. MMA current depends mainly on the electrode type and diameter, while TIG settings depend on the material and joint. Our TIG amperage table gives further guidance for TIG, and any specified welding procedure takes priority over these examples.
Welding Processes and Typical Thickness
| Process | Common materials | Practical thickness range |
|---|---|---|
| TIG | Steel, stainless steel, aluminium, copper and titanium. | Useful from thin sheet, around 0.5 mm with suitable equipment, through to thick multi-pass joints. Deposition rate can make thicker work slow. |
| MIG | Steel, stainless steel and aluminium. | Covers thin sheet around 0.7 mm with suitable control, through to heavy multi-pass fabrication. Capacity depends on the machine and procedure. |
| Flux-cored | Mainly steel and stainless steel. | Often chosen for work from about 3 mm upwards, although some wires suit thinner material. Check the wire’s recommended application. |
| MMA | Steel, stainless steel, cast iron and hardfacing applications with appropriate electrodes. | Generally easier from around 3 mm upwards; thinner work needs particular care. Thick joints can be welded in multiple passes. |
| Spot | Suitable steel, stainless steel and coated sheet, depending on equipment. | Capacity is specific to the machine, material and sheet combination. A 1.5 + 1.5 mm rating means two sheets of that thickness, not a universal process limit. |
Recommended Process by Material Thickness
| Thickness and application | Recommended | Why |
|---|---|---|
| Under 1.5 mm. Panels, trim and ducting | MIG with suitable fine wire, often 0.6 to 0.8 mm on steel, or spot welding for appropriate overlaps. | Good control at low output helps avoid burn-through. Vehicle repairs must follow the specified repair method. |
| 1.5 to 3 mm. Light fabrication and frames | MIG for productivity, or TIG where precise control and appearance are priorities. | The material, joint and finish help decide which process is more practical. |
| 3 to 6 mm. General fabrication and pipework | MIG with wire suited to the current, often 0.8 to 1.0 mm, or MMA. | MIG is productive in the workshop; MMA can be convenient outdoors. Both need suitable joint preparation. |
| 6 to 12 mm. Structural and heavy fabrication | MIG, flux-cored or MMA with a suitable welding procedure. | Preparation, fusion and pass sequence matter as much as maximum machine current. |
| Over 12 mm. Thick plate and industrial work | MIG, flux-cored or MMA, usually with multiple passes. | Deposition rate becomes an important part of productivity, alongside the joint’s technical requirements. |
| Thin stainless, aluminium and specialist alloys | TIG is often useful; choose AC/DC for routine aluminium TIG work. | It gives fine control of the weld pool, with AC providing oxide-cleaning action on aluminium. |
Power Supply and Machine Limits
Check the available supply before settling on a machine. The right connector is only part of the answer: the circuit also needs to suit the welder’s input current and the manufacturer’s protection requirements. An unsuitable supply can cause tripping, voltage drop or overheating, so confirm the installation before buying.
Extension Leads
An extension lead adds resistance between the supply and the welder. If it is too long or its conductors are too small, the resulting voltage drop can affect the machine’s output or make it shut down. A loaded cable reel can also overheat if it is left coiled, even when the machine appears to run normally.
- Use a suitably rated extension lead with the conductor size and maximum length specified for the machine, and keep the run as short as practical.
- Fully unwind a cable reel before welding. This lets heat escape and avoids relying on the much lower load rating that often applies while the cable is coiled.
- If you regularly need a long extension, ask an electrician about a suitable outlet closer to the work area.
Running From a Generator
- Check that the manufacturer permits generator use. Follow the stated supply-quality and warranty requirements, because unstable voltage can damage the power source.
- Size the generator for the welder’s input demand. Use the manufacturer’s recommended generator capacity, allowing for peaks, other loads and any derating. Check both kVA and kW ratings, and the output available on the phase you will use.
- Check voltage, frequency and waveform quality. An inverter or AVR generator may help provide a stable supply, but the label alone does not confirm compatibility with the welder.
- A welder-generator combines the engine and welding power source, which can simplify work away from the mains. Check the available welding modes, duty cycle and auxiliary power in our welder-generator range.
How Many Amps Does a Welder Draw?
Welding output current and mains input current describe different sides of the machine. A welder producing 200 amps at the torch does not need a 200 amp mains supply, because the voltage at the welding output is much lower than the supply voltage.
The power source converts the mains supply into the voltage and current needed for welding. Input current depends on the welding process, output voltage, efficiency and power factor as well as amperage, which is why two machines with the same maximum welding current can have different supply requirements.
The Two Figures on the Plate
- I1max is the rated maximum supply current under the specified conditions. It helps describe the machine’s input demand, but the correct fuse or breaker must be selected using the installation instructions and circuit requirements.
- I1eff is the effective supply current, which accounts for the heating effect of current over the duty cycle. It can be lower than I1max, but it is not a simple arithmetic average or a stand-alone rule for choosing cable size.
| Machine | Input-current check | Supply check |
|---|---|---|
| 130 to 160 A inverter, single phase | Check I1max and any output restrictions for a 13 A connection. | Use a 13 A plug only where the manufacturer permits it and the circuit is suitable. |
| 180 to 200 A inverter, single phase | Check the input figures for the process and output you intend to use. | Some models suit a 16 A circuit; others need more capacity. Follow the installation instructions. |
| 250 A inverter, single phase | Check I1max, I1eff and the specified fuse or breaker requirements. | Do not assume a 32 A outlet is sufficient for every model or workload. |
| 250 to 400 A, three phase | Use the manufacturer’s current figure per phase. | Confirm the stated voltage, phase arrangement, circuit capacity and protection. |
Use the table as a guide to what needs checking, rather than a way to calculate socket or breaker size. The specific machine’s rating plate and installation instructions are the starting point, with the complete circuit checked by a competent electrician.
- Power factor correction can reduce supply demand. PFC helps a machine use the available supply more effectively, although you still need to check its actual input ratings and permitted connection.
- Three-phase supplies share the load across three phases. This can reduce the current in each phase for a given output, which is one reason they are common in higher-powered production equipment.
- Check spot welders separately. Their short welding pulses can place a high peak demand on the supply. Give the electrician the model’s electrical data and expected welding rate before arranging the installation.
- Confirm any supply changes with an electrician before buying. Fitting a larger industrial socket only helps if the circuit and its protection are suitable for the machine.
Types of Welding Machine
By Process
| Type | What it does | Typical buyer |
|---|---|---|
| MIG welder | Feeds a continuous wire into the joint, normally with bottled shielding gas. | Fabricators, bodyshops and general workshops needing productive welding. |
| TIG welder | Uses a tungsten electrode to create the arc, with filler added separately when needed. | Stainless steel, aluminium, pipework and jobs needing precise control. |
| MMA welder | Uses flux-coated stick electrodes without a separate shielding-gas supply. | Site work, maintenance, farm repairs and outdoor jobs. |
| Multi-process | Combines several processes, commonly MIG, MMA and DC TIG; check the model’s exact capabilities. | Workshops handling varied jobs or needing a versatile first machine. |
| Spot welder | Joins overlapping sheets using electrode pressure and electrical resistance heating, without filler or shielding gas. | Sheet-metal production and suitable panel work. |
| Welder-generator | Combines an engine-driven welding power source with auxiliary electrical output. | Work away from a suitable mains supply. |
| Plasma cutter | Cuts electrically conductive metal using a concentrated plasma arc. | Workshops preparing their own material alongside welding. |
Inverter or Transformer
Inverter machines are common because they combine a relatively compact power source with a wide range of controls. Conventional transformer machines remain in use too, particularly in established workshops, so the differences below are useful when comparing new and second-hand equipment.
| Inverter | Transformer | |
|---|---|---|
| Weight and size | Usually more compact and lighter for a comparable output. | Usually larger and heavier for a comparable output. |
| Efficiency | Often more efficient, but compare the actual input ratings. | Efficiency and idle consumption vary with the design. |
| Arc control | Can offer pulse, synergic settings and electronic arc controls, depending on the model. | Traditional designs often have simpler controls; capabilities vary. |
| Robustness | Requires suitable protection from dust, moisture and physical damage. | Some designs are mechanically simple, but still need protection and maintenance. |
| Availability | A common choice across portable and workshop machines. | Still found in specialist equipment and the second-hand market. |
Other Choices That Affect the Price
- Synergic or manual MIG. Synergic controls link settings such as voltage and wire speed for the selected wire and gas, making setup quicker. Some also let you start from material thickness, with adjustments available to suit the joint.
- Pulse and double pulse. Pulsed MIG can provide spray transfer at a lower average current, helping with heat control. Double pulse varies the output further and can produce a regular ripple pattern, particularly on aluminium.
- Air-cooled or water-cooled torch. Water cooling becomes useful as current and arc-on time increase, often allowing a smaller torch for sustained work. Compare the torch’s rating for your process and gas rather than using a fixed amperage threshold.
- Integrated or separate wire feed. A separate feeder lets you move the wire supply nearer a large fabrication while leaving the main power source in place.
- AC/DC or DC-only TIG. For routine aluminium TIG work, choose AC/DC from the outset. Most DC-only machines cannot be upgraded to provide AC simply by adding a torch or accessory.
Process-Specific Considerations
MIG
- Look at how the wire-feed system handles the wire you intend to use. Four-roll drives offer more grip, which can help with soft wire and longer torch leads, but correct rolls, tension and liner condition matter too.
- For aluminium, a spool gun or push-pull torch can make feeding more reliable. Some machines also support a short, properly equipped push-feed setup; check compatibility and use the specified liner, rolls and contact tip.
- Check both spool diameter and weight capacity. A compact machine may accept only smaller reels, which affects the sizes you can buy and how often you need to change them.
- If you want to use self-shielded, or “gasless”, flux-cored wire outdoors, check that the machine supports the wire and its required polarity. Many wires need electrode negative, but follow the wire manufacturer’s instructions.
TIG
- For routine aluminium TIG welding, look for an AC/DC machine with adjustable AC balance and, where useful, frequency. These controls help you balance oxide cleaning with arc shape and penetration.
- HF start lets you strike the arc without touching the tungsten to the work. Lift start uses controlled contact, while scratch start is more prone to contamination, so check which starting method the machine provides.
- Check whether a foot pedal or torch-mounted remote is supported if you want to adjust current while welding, and whether the control is included or sold separately.
- Adjustable pre-flow and post-flow help protect the weld and tungsten with gas, while downslope reduces current gradually to help fill the end crater.
- Match the duty cycle to the length of your TIG runs. Longer welds need both the power source and torch to sustain the required current without overheating.
MMA
- Hot start briefly boosts current when striking the arc, while arc force helps prevent sticking as the arc becomes short. These functions can make some electrodes easier to use.
- Check the machine’s compatibility with your electrode type, including its open-circuit voltage and arc characteristics. Cellulosic electrodes can be particularly demanding, so a high maximum amperage alone is not enough.
- A voltage reduction device, or VRD, lowers the open-circuit voltage when you are not welding. It can reduce shock risk and may be required by site rules, but does not make wet or confined-space work safe on its own.
- A compact MMA machine can be a practical second set for repairs and work away from the main welding bay, especially when portability matters more than deposition speed.
Spot Welding
- Check how the spot-welding thickness rating is written. A rating of 2 + 2 mm means two 2 mm sheets; confirm the material, coatings and sheet combination it covers rather than relying on total thickness alone.
- Look for control of electrode force, current and weld time so you can establish and repeat settings suited to the joint.
- Check the arm length, shape and available electrode force together. The electrodes need to reach the joint and clamp it properly in the configuration you will use.
- For production work, check the cooling requirements and welding rate. Suitable water cooling helps control electrode temperature and wear during repeated welding.
Reading the Rating Plate
The rating plate gives you the electrical information needed to check a machine against your work and supply. On arc-welding power sources marked to EN 60974-1, the following symbols are commonly used; read them alongside the installation instructions, which explain how they apply to that model.
| Marking | Meaning | Why it matters |
|---|---|---|
| I2 / X | Welding output current and the duty cycle at that current. | Compare the figures at the output and test temperature relevant to your work. |
| U0 | Open-circuit voltage, present before the arc is struck. | Relevant to arc starting, electrode compatibility and electrical safety. |
| U1 / I1max / I1eff | Supply voltage, rated maximum supply current and effective supply current. | Read these with the installation instructions when checking the circuit and protective devices. |
| IP rating | The enclosure’s tested protection against solid objects and water. | IP23S does not mean waterproof. Follow the model’s restrictions on rain, moisture and outdoor use. |
| S mark | Indicates a power source suitable for welding in an environment with increased electric-shock risk. | It does not make damp or confined-space work safe on its own; the work still needs suitable controls. |
| Single or three phase symbol | The supply arrangement the machine supports. | Use only the stated options. Some models support both, but a three-phase-only machine cannot simply be connected to single phase. |
Compare duty cycle at the current you actually need. A 250 amp machine rated at 40% and a 200 amp machine rated at 60% may perform similarly at your working output, but their maximum-output figures do not prove that. Look at each machine’s ratings or duty-cycle chart at the same current and test temperature.
What Else to Check Before You Buy
- Consumable cost and availability. Compare the price and availability of tips, shrouds, liners and replacement torches, including whether they use common fittings or parts specific to that machine.
- Spares and service. Ask who carries out repairs in the UK, which parts are stocked and how long the manufacturer expects to support the model.
- Read the warranty terms for the work you intend to do, including generator use, operation beyond the rated duty cycle and the cover provided for the torch.
- Consider the complete working weight if you move between jobs. The power source may be compact, but the wire, gas cylinder, torch and cables all add to what you need to transport.
- Compare gas-cylinder arrangements. Rental, refillable ownership and disposable cylinders have different costs, so choose around the amount of welding you expect to do.
- Check torch length and cable reach against your work area. Enough reach reduces machine movements, but longer leads must still suit the wire-feed system and electrical requirements.
- Allow for likely future work. A little extra capacity or a useful additional process may be worth buying now if it avoids replacing the machine as your workload grows.
Quick Selection Reference
| What you do | Process | Machine | Supply |
|---|---|---|---|
| Car bodywork and thin sheet | MIG, or spot welding where the repair method allows. | For MIG, a 150–180 A class machine with stable low output; check duty cycle. | 13 A only if the model and intended use permit it. |
| General workshop fabrication | MIG or multi-process. | 200–250 A class; around 40% or more at the working current for intermittent work. | 16 A or 32 A may suit; check the model. |
| Stainless and aluminium fabrication | TIG; AC/DC for routine aluminium work. | Around 200 A for lighter work, with capacity and duty cycle to suit the thickest joint. | Check the input ratings and installation instructions. |
| Structural steel and heavy plate | MIG, flux-cored or MMA. | Often 300 A class or larger for productivity; around 60% or more at the working current. | Three phase is common; confirm voltage and current. |
| Site and maintenance work | MMA or self-shielded flux-cored. | A portable 160–200 A class machine for many repairs; check electrode capacity and weather restrictions. | A suitable mains circuit or compatible generator. |
| Panel-shop production | Resistance spot welding. | Match capacity, reach and electrode force to the materials and sheet combination. | Check peak demand and welding rate. |
| Varied work across several processes | Multi-process. | 200 A class is a starting point; check the included modes, controls and accessories. | Follow the model’s supply and protection requirements. |
Choosing a Welding Machine FAQ
What amp welder do I need?
Start with the process, material and joint rather than thickness alone. For mild steel MIG, roughly 40 amps per millimetre is a useful starting estimate on thinner material, putting 3 mm steel around 120 amps. Use the machine’s settings guide or welding procedure to refine that figure. MMA current depends mainly on the electrode, and thicker joints may need preparation and multiple passes. Check duty cycle as well as maximum output.
How many amps does a welder draw from the mains?
The input current is different from the welding current because the machine converts mains power to a much lower welding voltage. The amount drawn depends on the process, output, efficiency and power factor, so there is no reliable conversion from the amperage on the front panel. Check I1max, I1eff and the manufacturer’s installation requirements for the particular model.
What does duty cycle mean on a welder?
For an arc welder, duty cycle is normally the percentage of a ten-minute period it can weld at a stated current under its rated conditions. A rating of 200 A at 40% means four minutes of welding followed by six minutes of cooling. Lower current usually allows longer welding time, but use the published rating to check continuous output. Compare ratings at the same current and test temperature.
Can I run a welder from a 13 amp plug?
Some machines are designed for a 13 amp plug, sometimes with restrictions on output or duty cycle. There is no universal welding-amperage limit that proves a machine is suitable. Check the manufacturer’s connection instructions and have the circuit confirmed as suitable. A plug that fits, or a welder that starts, does not establish that the supply can support the intended workload.
Can I run a welder off a generator?
Often, provided the manufacturer allows it and the generator meets the welder’s requirements for capacity and supply quality. Use the recommended generator size and allow for other loads and any derating. An AVR or inverter label alone does not guarantee compatibility. A welder-generator combines the two systems, but you still need to check its welding modes, duty cycle and auxiliary output.
MIG, TIG or MMA: which should I buy first?
MIG is a practical starting point for general steel fabrication because it is relatively easy to learn and productive. TIG suits precise work and visible welds, with AC/DC the usual choice for aluminium TIG. MMA is useful for outdoor work and repairs where bottled shielding gas is inconvenient. If your jobs vary, compare multi-process machines, checking exactly which modes and accessories each includes.
Why does my welder keep cutting out?
Check the warning display or fault code first. A thermal warning may mean the duty cycle has been exceeded or cooling is restricted; let the machine cool as the manual directs and check airflow. Supply faults, voltage drop and equipment faults can also cause shutdowns. Do not keep resetting a tripping circuit or reduce current below what the weld needs simply to keep working.
Do I need AC/DC TIG or is DC enough?
DC TIG suits steel, stainless steel and many other metals. For routine aluminium or magnesium TIG welding, AC/DC is the practical choice because AC provides oxide-cleaning action as well as heat for fusion. Specialist DC aluminium techniques exist, but they are not a general substitute when choosing a workshop machine. Most DC-only models cannot be converted to AC with an add-on accessory.
Conclusion
To bring the choice together, work through these four questions before making your shortlist:
- What will you weld, and how thick is it? Use the material and joint details to choose a suitable process and output range.
- How much welding will you do between pauses? Check the duty cycle at the current the job requires, including the torch’s capacity.
- What supply is available? Confirm that the machine can run from it, or include the cost of any necessary electrical work.
- How might your work change over the next few years? Allow useful room to grow without paying for capacity or features you are unlikely to use.
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For help narrowing down the options, Tell us what you weld, how thick and what supply you have and we can help you compare suitable machines. Once you have chosen, our guides to MIG wire, TIG filler rods and fume extraction will help you select the consumables and supporting equipment.
