A 240 V welder that draws 30 A needs a generator of about 8,400 to 11,500 running watts. That is 1.16 to 1.6 times its 7,200 VA input (240 × 30), the ratios behind the generator sizes ESAB and Miller state for their own machines; 7,200 W is only the bare minimum. To work out what size generator to run a welder of your own, enter its input volts and amps below. You get the range, what Miller, ESAB and Lincoln manuals say, whether a 30 A or 50 A generator outlet can pass the current, and what a generator you already own can feed.

Compiled by Welding Tribe from the published sources listed below. Numbers last updated on November 12, 2026.

Size a generator for your welder

Enter the input volts and rated input amps from the welder’s nameplate. You get the running watts it draws, what welder makers ask for on top, and whether the generator’s outlet can pass it. Add the generator you own to see what it can feed.

8,400–⁠11,500 W

running (rated) watts for a 240 V welder that draws 30 A. From ESAB’s and Miller’s generator sizes for their own machines: not a universal rule.

Bare minimum7,200 WArithmetic only, with no margin. It may not run the welder correctly.
Other loads and altitudeNone countedEnter other loads or your altitude above if they apply.
Generator outlet7,200 VAWhat a 30 A outlet passes at 240 V: enough for 30 A.
The generator you have
Go by running (rated) watts, not surge. Run a generator outdoors only, and never backfeed a building’s wiring.

Show the working

240 V × 30 A = 7,200 VA for the welder.
Bare minimum: 7,200 running (rated) watts, with no margin. ESAB warns that a generator without enough power may keep the welder from working correctly.
ESAB asks for 8 kW for a welder that draws 6.9 kVA, and Miller for 12 kW where the welder draws 7.5 kVA: 1.16 and 1.60 times the volts × amps sum.
The range: 7,200 W × 1.16 = 8,400 W (rounded up to the next 100) and 7,200 W × 1.60 = 11,500 W (to the nearest 100).
No maker we found gives one margin for every welder, so a figure in your own manual wins.
If the welder’s plug does not fit the generator’s outlet, use the plug or adapter cord the welder’s maker lists; Miller, for one, lists an optional plug for this.
Read your welder’s manual for a generator section: some makers set conditions, and Lincoln warns that a generator outside its voltage and frequency limits may damage the machine.
A connection to a building’s wiring must be made by a qualified electrician and must isolate the generator from utility power.

What size generator to run a welder: chart

The running watts to look for in a generator, by the welder’s rated input amps. The range applies the two ratios we found in welder makers’ manuals: the generator sizes ESAB and Miller state for their own machines, set against those machines’ volts × amps. It is not a universal rule, and no maker we could open gives one margin for every welder. The bare minimum is the plain sum, input volts times input amps, with no margin: do not shop by it.

Generator running watts for a welder, by rated input amps
Welder input amps	120 V: generator to look for	120 V: bare minimum (volts × amps)	240 V: generator to look for	240 V: bare minimum (volts × amps)
15 A	2,100–⁠2,900 W	1,800 W	4,200–⁠5,800 W	3,600 W
20 A	2,800–⁠3,800 W	2,400 W	5,600–⁠7,700 W	4,800 W
25 A	3,500–⁠4,800 W	3,000 W	7,000–⁠9,600 W	6,000 W
30 A	4,200–⁠5,800 W	3,600 W	8,400–⁠11,500 W	7,200 W
35 A	4,900–⁠6,700 W	4,200 W	9,800–⁠13,500 W	8,400 W
40 A	—	—	11,200–⁠15,400 W	9,600 W
45 A	—	—	12,600–⁠17,300 W	10,800 W
50 A	—	—	14,000–⁠19,200 W	12,000 W

Use the input amps on the nameplate, not the welding amps. Welding below full output draws less, and many manuals list the input amps at a lower output too. Anything else on the generator at the same time, such as a grinder or lights, adds its watts to the sum.

Wiring a fixed outlet instead? See the welder breaker size chart, which also sizes the extension cord. The welding cable size chart sizes the leads on the output side, and the stick welding amperage chart and MIG welding settings chart show the welding amps a job really needs.

What welder makers say about generators

From the owner’s manuals we could open. Two name a generator size, one sets limits on the power instead, and one says nothing. Miller’s Millermatic 211 manual has no generator section either.

Generator requirements in welder owner’s manuals
Welder	Input at rated output	Volts × amps	Times the sum	What the manual says
ESAB Rebel EMP 215ic	30 A at 230 V	6,900 VA	1.16	A generator with automatic voltage regulation (AVR), or regulation as good or better, rated 8 kW. Some generators may not give enough power for the welder to work correctly.
Miller Multimatic 235	31.2 A at 240 V	7,488 VA	1.60	For maximum output, a generator of 12 kW or greater. On a Miller welder/generator: engine control at RUN, not RUN/IDLE, and the voltage control at maximum.
Lincoln Invertec V155-S	33 A at 230 V	7,590 VA	—	No size named: the generator must supply adequate voltage, frequency and power. Peak voltage below 410 V on 230 V input (205 V on 115 V), frequency 50 to 60 Hz, voltage within 10%. Many engine-driven generators make high voltage spikes; one outside these limits may damage the machine.
Hobart Handler 210 MVP	24 A at 230 V	5,520 VA	—	No generator section in the manual.

Volts × amps is not the same as watts

A welder’s real power in watts is its volts × amps times its power factor, and the power factor is below 1. The generator still has to push the full current through its windings, outlet and breaker, so size it on volts × amps. Makers that print both figures show the gap.

Apparent power, real power and power factor at rated output
Welder	Volts × amps	Real power	Power factor
ESAB Rebel EMP 215ic	6.90 kVA	—	0.98 (stated; power factor corrected)
Lincoln Invertec V155-S	7.59 kVA	5.00 kW	0.66 (worked out)
Hobart Handler 210 MVP	5.54 kVA	4.72 kW	0.85 (worked out)

What a generator can feed

Running watts divided by volts gives the amps a generator can supply. Honda’s EU7000is manual shows the same sum: 5.5 kVA rated is 45.8 A at 120 V or 22.9 A at 240 V. A single outlet passes no more than its own rating: 30 A is 7,200 VA at 240 V, whatever the generator’s label says.

Amps a generator can supply, by running watts
Running watts	Amps at 120 V	Amps at 240 V
3,500 W	29.2 A	14.6 A
5,000 W	41.7 A	20.8 A
5,500 W	45.8 A	22.9 A
6,500 W	54.2 A	27.1 A
7,500 W	62.5 A	31.3 A
9,000 W	75.0 A	37.5 A
10,000 W	83.3 A	41.7 A
12,000 W	100.0 A	50.0 A
15,000 W	125.0 A	62.5 A

Generator power at altitude

An engine makes less power in thin air. Lincoln’s engine-driven welder manuals put the loss at 3.5% for each 1,000 ft (305 m) above 377 ft (115 m). The chart and the calculator take 3.5% per 1,000 ft from sea level, slightly on the safe side. Your generator’s own manual may give its figure.

Generator power left at altitude (3.5% lost per 1,000 ft)
Altitude	Power left	A 7,500 W generator gives about
Sea level	100%	7,500 W
2,000 ft (610 m)	93%	6,980 W
4,000 ft (1,220 m)	86%	6,450 W
5,000 ft (1,520 m)	82.5%	6,190 W
6,000 ft (1,830 m)	79%	5,930 W
8,000 ft (2,440 m)	72%	5,400 W
10,000 ft (3,050 m)	65%	4,880 W

Quick answers

What size generator do I need to run a welder?

Multiply the input volts by the rated input amps on the welder’s nameplate, then allow a margin. A 240 V welder that draws 30 A takes 7,200 VA. ESAB and Miller state generator sizes for their own machines that are 1.16 and 1.60 times that sum, so look for about 8,400 to 11,500 running watts. 7,200 W is only the bare minimum. If your manual names a generator size, use that.

Will a 5,000 watt generator run a welder?

A small one, yes. 5,000 running watts is 20.8 A at 240 V or 41.7 A at 120 V. That covers a machine such as Miller’s Millermatic 211, which draws 16.6 A at 240 V: about 1.3 times its sum, inside the two makers’ range. It cannot run a welder that draws 30 A at 240 V at full output, which takes 7,200 W before any margin.

How many watts does a welder use?

Input volts times input amps, at the output you weld at. At rated output on 230 or 240 V: Miller’s Millermatic 211 draws 3,984 VA (16.6 A), Hobart’s Handler 210 MVP 5,540 VA (24 A), of which 4,720 W is real power, and Miller’s Multimatic 235 7,488 VA (31.2 A). Turned down, a welder draws less.

Can you run a welder off a generator?

Yes, if the generator is big enough and its power is clean enough for the machine. Miller asks for 12 kW or more to get full output from its Multimatic 235. ESAB asks for 8 kW with automatic voltage regulation for its Rebel EMP 215ic. Lincoln says its Invertec V155-S runs on engine-driven generators that hold the voltage and frequency within limits. Check your manual before you plug in.

Will any generator with a 240V outlet run my welder?

No. Three things have to be true. Its running watts cover the welder’s volts × amps. Its outlet and breaker pass the welder’s input amps: a 30 A outlet stops at 30 A. And its power suits the machine: Lincoln’s limits for the Invertec V155-S on 230 V are a peak voltage below 410 V, 50 to 60 Hz and a voltage within 10%, and it warns that many engine-driven generators make voltage spikes.

What size generator for a 120V welder?

Work it the same way. Miller’s Millermatic 211 draws 24.3 A on 120 V at rated output. At the two makers’ ratios that is a generator of about 3,400 to 4,700 running watts; the bare minimum is 2,916 W. A 120 V outlet on the generator must also pass that current: a 20 A outlet stops at 20 A.

Running watts or starting watts: which one counts?

Running watts, also called rated watts. A welder draws its input amps for as long as the arc is on, so the surge figure does not help. Honda’s EU7000is, for example, has a maximum output of 7.0 kVA but a rated output of 5.5 kVA, which is 22.9 A at 240 V. Its manual says a load must not exceed the rated power or the outlet’s current limit.

Why size on volts × amps and not on kilowatts?

Because of power factor. Lincoln’s Invertec V155-S draws 33 A at 230 V, which is 7,590 VA, to use 5,000 W of real power. Hobart’s Handler 210 MVP draws 5.54 kVA to use 4.72 kW. The generator’s windings, outlet and breaker carry the full current either way. Welders with power factor correction, such as ESAB’s Rebel EMP 215ic at 0.98, close the gap.

Does altitude change the generator size?

Yes. Lincoln’s engine-driven welder manuals put the loss at 3.5% of engine power for each 1,000 ft. At 5,000 ft that is about 17.5%, so a 7,500 W generator gives about 6,190 W. Buy or rent the next size up for mountain work.

Can I run the welder by plugging the generator into the house?

Not through an outlet, ever: that backfeeds the utility lines and can kill a line worker. Honda’s manual says a connection to a building must be made by a qualified electrician and must isolate the generator from utility power. Plug the welder into the generator itself.

Ground and bond a portable generator as its own manual says. The sum works on any supply, but this page uses North American voltages (120 and 240 V); elsewhere, use the volts on your nameplate and your generator’s rated output in kVA.

Generator sizes and conditions: the generator sections of Miller’s Multimatic 235 owner’s manual, ESAB’s Rebel EMP 215ic instruction manual and Lincoln’s Invertec V155-S operator’s manual. Stated in our own words.
Input amps, kVA and kW: the same manuals, plus the unit specifications in Hobart’s Handler 210 MVP and Miller’s Millermatic 211 owner’s manuals. Power factors marked “worked out” are kW divided by kVA.
Rated output against maximum output, amps from rated output, outlet limits and safety: Honda’s EU7000is owner’s manual.
Altitude: “High Altitude Operation” in Lincoln’s Weldmark 225 engine-driven welder manuals (IM851 and IM806).
The range to look for is our own arithmetic from the two generator sizes above (ESAB’s and Miller’s, set against their machines’ volts × amps). It is not a published rule.

Numbers compiled from the sources below and last updated on November 12, 2026. Spotted a mistake? Tell us.

What Size Generator to Run a Welder? Calculator