What Size Generator Do You Need to Run a Welder?
By the Generator Size Calculator Team · Updated · 6 min read
Quick answer: Honda lists an electric welder at 2,800 watts for 70 amps, 3,600 watts for 100 amps and 9,000 watts for 200 amps. Welders have no big start-up surge, but they draw high power the whole time you weld. Keeping the load under 80% of the rating suggests about a 3,500-watt generator for a 70-amp welder, 4,500 watts for 100 amps and 12,000 watts for 200 amps. Check the label on your welder, because the real draw depends on its input.
Welder watts by amperage
| Electric welder | Running watts | Starting watts |
|---|---|---|
| 70 amp | 2,800 | 2,800 |
| 100 amp | 3,600 | 3,600 |
| 200 amp | 9,000 | 9,000 |
Starting watts match running watts in Honda's guide, so there is no extra surge to add. That makes sizing simpler than for motor tools, but the load is heavy and continuous while you weld.
Which generator size to choose
| Welder | Load | Generator at 80% |
|---|---|---|
| 70 amp | 2,800 W | About 3,500 W |
| 100 amp | 3,600 W | About 4,500 W |
| 200 amp | 9,000 W | About 11,250 W, so use 12,000 W |
The 80% rule means the running load should stay under about 80% of the rated output, so divide the welder's watts by 0.8. Add a little more if you also run a grinder or lights. See the grinder and saw numbers in what size generator a workshop needs.
Check your welder's label
Honda's figures are typical. Your welder's input rating, in amps at 120 or 240 volts, is the real number, and many welders draw much less than their output amps because the input voltage is higher. Multiply input amps by input volts to estimate watts, and use the generator amps calculator. Some welders also need a 240-volt receptacle, so check the generator's outlets.
Add the welder, a grinder and lights to see the generator size.
Tips for welding on a generator
- Choose a generator with a good 240-volt output if the welder runs on 240 volts.
- Use a short, heavy cord. Long thin cords cause voltage drop. See the voltage drop calculator.
- Check the manual for generator requirements. Some welders specify minimum generator size or clean power. See inverter vs conventional generators.
- Keep the generator away from sparks and fumes, in a spot with fresh air.
Run the generator outdoors, at least 20 feet from doors, windows and vents. Never in a garage or shed, even with the door open. See how far a generator should be from your house.
Frequently asked questions
What size generator do I need for a 100 amp welder?
Honda lists a 100-amp electric welder at about 3,600 watts. At the 80% rule that suggests a generator of about 4,500 watts.
Can a 3500-watt generator run a welder?
A 70-amp welder at about 2,800 watts, yes. A 100-amp welder at 3,600 watts is more than a 3,500-watt generator can supply.
Does a welder have a start-up surge?
Honda lists the same starting and running watts for an electric welder, so there is no extra surge. The load is high and steady while welding.
Can I run a welder on an inverter generator?
Some people do, but check the welder manual for any generator requirements and make sure the inverter has enough continuous watts.
How do I find my welder's real watts?
Check the input rating on the label. Multiply input amps by input volts, or measure with a watt meter.
Related calculators
Sources: Running and starting watts from the Honda generator wattage guide (electric welders). Generator sizes apply the 80% running-load rule. Real draw depends on the welder's input rating, so check your label.