Calculate welding machine load in kW from input voltage, current and power factor for single- or three-phase supply, plus energy use over time.

For three-phase, enter line-to-line voltage and line current.

Typical values; use the PF on your machine’s rating plate if known.

Optional settings
Optional. Blank omits energy. Excludes energy used at other power levels.

Welding Machine Load Formula

For welding equipment, the term load is commonly used in two ways: the machine’s real electrical input at a specific moment, and the total electrical energy it uses over time. The calculator fields for voltage, current, power factor, and power help you determine the real input power first. From there, you can estimate total energy use in kilowatt-hours.

Real Input Power

P = V × I × PF

For single-phase AC, this equation gives real input power in watts from RMS input voltage, RMS input current and true power factor. For balanced three-phase input, P = √3 × V × I × PF, using line-to-line voltage and line current.

Total Energy Used

WML = P × t / 1000
WML = V × I × PF × t / 1000

These forms give energy in kilowatt-hours during time spent at the stated input power. Add idle and other operating periods separately for total consumption; arc-on time alone omits idle energy.

Rearranged Forms

V = P / (I × PF)
I = P / (V × PF)
PF = P / (V × I)

These relationships are useful when the calculator is solving for a missing input value.

Variable Definitions

Symbol Description Common Unit
V Input voltage supplied to the welding machine V or kV
I Input current drawn by the machine A or kA
PF Power factor of the electrical input Unitless
P Real input power W or kW
t Operating time hours
WML Total welding machine load as energy consumed kWh

How to Calculate Welding Machine Load

  1. Enter the machine’s input voltage.
  2. Enter the input current draw.
  3. Choose a welder type for a typical power factor, or pick Custom and enter it as a decimal.
  4. Use the calculator to determine real input power in watts.
  5. Optionally enter time at this input power to calculate energy. Add any idle or other operating periods separately.

Example

Suppose a welding machine draws 240 V, 30 A, and has a power factor of 0.85. If it runs for 2.5 hours, first calculate the real input power:

P = 240 × 30 × 0.85 = 6120

The machine’s real electrical load is 6120 W, or 6.12 kW.

Next, calculate the total energy used during operation:

WML = 6120 × 2.5 / 1000 = 15.3

In this case, the welder uses 15.3 kWh of electrical energy over 2.5 hours.

What Affects Welding Machine Load?

  • Voltage: Supply voltage changes the relationship between current and power.
  • Current draw: Higher current increases the electrical demand on the supply.
  • Power factor: Real power is lower than simple volt-amp multiplication when the power factor is below 1.
  • Operating time: Longer use increases total energy consumption even when power stays constant.
  • Machine setting and duty cycle: Higher output settings and longer active welding periods usually increase overall consumption.

Practical Notes

  • Use the welder’s input electrical data, not the welding output rating, when estimating supply load.
  • For intermittent use, estimate each operating and idle period using its corresponding input power; a single full-load figure does not describe the whole shift.
  • This calculator is best suited to the simple voltage-current-power factor relationship shown above.
  • If your welding machine uses a different supply arrangement, confirm that the input values and method match the equipment.
  • This estimate does not size circuits, breakers or generators. Follow the equipment instructions and applicable electrical requirements.

Common Questions

How many watts does a welder use?
A welder has no universal wattage based only on its welding output amps or process. Input power varies with the exact model, supply, welding setting and efficiency. Use the input ratings for that operating point in the manual or on the rating plate; output amps are not supply amps. If a rating is in kVA, multiply by its true power factor to obtain kW. A duty-cycle percentage describes allowable welding time at a stated output, not a direct conversion from output amps to input watts.
Is welding machine load the same as power?
Sometimes. Many people use load to mean the machine’s instantaneous input power in watts or kilowatts. Others use it to mean total energy consumption over time in kilowatt-hours.
What if I already know the power?
You can skip the voltage and current relationship and calculate energy use directly from power and operating time.
Why does power factor matter?
Power factor adjusts the difference between apparent electrical demand and real power actually consumed by the machine.
Can this help estimate electricity usage?
Yes. Once real power is known, converting that value into kilowatt-hours provides a practical estimate of energy consumed during operation.