How to Choose The Right Generator Size For Your Welding Needs

Practical usability, total portability, and power backup are the three most common factors that every welder consider when purchasing a power generator.

Erratic power supply has bugged amateurs and professionals alike at some point. For those with work areas outside the state power supply limits, finding the right generator for a welder is essential.

We can all acknowledge that for any project to be successful and to enable us to utilize our skills to the hilt, we require the right tools, gear, and an uninterrupted power supply. All three need careful consideration, in-depth research, and deliberations when choosing our pick.

While our work area determines the tools of choice, the selection of the right gear is subject to our comfort and utility. However, zeroing in on the perfect gen set is solely dependent on the welder we plan to power.

If you are reading this, you are most likely looking to buy a new generator for your welder or might be interested in acquiring some knowledge about welder gen sets, whatever the case may be, keep on reading.

This article will cover everything that you need to know about picking the right sized generator for your welder.

Suggested Minimum Generator Size

Welder Max. OutputIdeal Generator
  Up to 160A8+kva

What generator size do I need to run a welder?

The size of the generator depends on the features of the welder. Welders generally run with an output voltage of 120-volt or with 240-volt.

In some welders, you will find both features. You have to calculate the power consumption of the welder using the input current and input voltage. Just choose a welder generator combo that is rated with an output power more than the required power of the welder.

size generator of welder

Editor’s choice: Perfect generator for you

Key factors and considerations when choosing the ideal generator for welding

Most welders– professionals and amateurs alike, lay more emphasis on identifying the correct wattage when choosing a generator for a welder while entirely overlooking the other factors that compliment the right sized generator. 

The generator needs to function smoothly to ensure that the welder’s performance is optimal. 

Simply put, a generator is a machine that converts mechanical energy into electrical energy. A portable generator uses fuel to produce and supply electricity. As the name suggests, it’s compact and is a temporary power source.

• The difference in the quality of current flow

Power supply from the mains

The power supply from the AC mains is devoid of fluctuations. The voltage is constant without any rise or sudden peaks. It is safe for all kinds of power tools and welders. It enables any welder to perform smoothly and safeguards against circuit breaks and overloading.

Power supply from the generators

Power supply from the portable generators can fluctuate with surges and spikes. This, without a doubt, can be harmful to welders. The sudden rise and fall in voltage can adversely affect the performance and functioning of the welder. It is increasing the chances of overloading and circuit breaks.

• Additional features complimenting the right sized generator

Low THD value:

THD or Total Harmonic Distortion is the measurement of the deviation in power supply from the normal. Generators with or less than 6% THD are considered high-quality generators. The lower THD ensures power supply without significant fluctuations or spikes and surges. They are ideal for power tools and Welders.

Fuel meter/display: 

As generators use fuel to produce electricity, low fuel levels can drastically lower the power supply. In case the fuel runs out entirely, it might end up damaging the welder and the generator. Thus, constant monitoring of fuel levels is mandatory. A fuel meter or display is highly useful to safeguard against low or empty fuel tanks.

Low maintenance: 

The performance of any generator depends on the quality of its maintenance support. Thus, a generator that requires high maintenance will perform poorly if not attended regularly. A high-performance generator with low maintenance can be a wise option.

The right wattage of a generator does not entirely determine the smooth operation of the welder. In addition to the correct size, the quality of the power supply is crucial for smooth functioning.

Determining the right generator size: understanding welder input voltage and output amperage

Now, let’s get to the most vital phase in choosing the right generator for your welder. The versatility of the welder determines the input voltage and the output amp.

In most cases, a welder that supports TIG, MIG, Stick welding, and grinding is bound to require more power input to produce the output needed to support all functions. On the other hand, a basic stick welder will require lesser input voltage to power the singular purpose.

The input voltage and the output amp together determine the required wattage to power any welding unit. For inverter welders, some additional factors come into play when deciding the right wattage.

Common folly when deciding the size of the generator

Fixing the wattage of a generator first without identifying the amount of power required to operate a welding unit is far from being wise.   

So the following take when deciding on the size of the generator is inconclusive:

How big of a generator do I need to run a welder?

The size of a generator to run a welder depends on the required power of the welder. For this, you need to calculate the total wattage of the welder by the following formula:

Power Voltage (V) × Input Current (A) = Power (watts)

You will find the power voltage and the input current on the label of the welder. Use this value for finding the appropriate generator.

1. Will a 3000-watt generator run a welder?

If the wattage of the welder is less than 3000 watts, then the welder can be run by a 3000-watt generator. Most of the small 120-volt welders with maximum output less than 120 amps can be run using the generator with 3000 running watts.

2. Will a 5000-watt generator run a welder?

If the wattage of the welder is less than 5000 watts, then the welder can be run by a 5000-watt generator. The generator with 5000 peak watts can run a 120-volts welder with maximum output under 160 amps.

3. Will a 4000-watt generator run a welder?

If the wattage of the welder is less than 4000 watts, then the welder can be run by a 4000-watt generator. Most of the small 120-volt welders with a maximum output of less than 120 amps can be run using a 4000-watt generator.

What size generator to run 140 amp welder?

If the power voltage of the 140 amp welder is 120-volt, then the input current will be less than 30 amps. In some cases, the welder needs input current close to 40 amps. A generator having running watts in between 3600 and 4800 will be required to run a 140 amp welder.

What size generator do I need to run a 220v welder?

Knowing only the power voltage, in this case, 220v is not enough to answer this question. The required power depends on both power voltage and inputs current. For example, if the input current for this particular welder is 45 amps then, the generator must be rated at 9900 running watts.

How to choose a generator for inverter welders

If the welder in question is an Inverter Welder, with wattage less than 3000W, the 3000W generator will not run it.

Without a doubt, this contradicts the principle of welders requiring equal or slightly higher wattage generators. As an inverter welder will require a generator that produces at least 1.5 times more power.

This is because of the fact that inverter welders utilize the input power to charge and discharge current with the help of Capacitors continually. These electrical components use approximately 1.4 times more input voltage than a regular welder. Thus, if the input voltage is 120 V, an inverter welder will require 168 V.

Thus, an ideal generator for any inverter welder is the one with wattage 1.5 times higher than the required input voltage.

How to find out the right-sized generator for any welder

Calculate the wattage of the welding unit. The general rule of the thumb to determine the wattage is as follows:

Input voltage * output amp = wattage

So, a welder with an input voltage of 110V and output of 25 amps will have the wattage of:

110 V * 25 Amps =2750 W

Thus, in the above scenario, any generator with a power greater than 2750 W can run the welder.

In the case of an inverter welder, add 1.5 times to the wattage.

Most experienced welding professionals agree that an ideal generator for any welding unit must have a higher wattage than the minimum requirement, to safeguard the group against fluctuations, overloading, and tripping.

The bottom line is while deciding on the generator; make sure you determine the wattage of the welder first.

Frequently asked questions (FAQs)

Q. How many watts does a 90 amp welder use?

A 90 amp welder uses about 1700 watts. A generator that has a running watts more than 1700 can run a 90 amp welder.

Q. Will a 3 KVA generator run a welder?

A 3kva generator will run a welder, but the wattage of the welder must be under 3000 watts. Most of the small 120-volt welders within maximum output of 120 amps can be run using a generator having 3000 running watts.

Q. Can you run a stick welder on a generator?

Yes, you can run a stick welder on a generator.

Q. What size generator to run a mig welder?

To run a MIG 140 and MIG 170 at an input voltage of 120V, a generator having 3000 running watts is needed. To run a MIG 170 at an input voltage of 240V, a generator consisting of 6500 running watts is needed.


The size of the generator matters when you are going to use it in welding. And hopefully, you will have no query on what size generator do I need for a welder after reading this article.

You know the generator comes in different sizes. And not every size is appropriate for every type of welding. So you have to consider the types of welding before choosing a generator for your welding task.