Welding Power Consumption and Cost Calculator
Sizing a supply, a generator or a power budget for welding starts with input kilowatts and kVA, not the number on the dial. This calculator converts arc volts and amps into input power, supply current and monthly electricity cost.
Your numbers
Inverters are often 80 to 90 percent; older transformer sets are lower.
Inverters with correction are near 0.9 to 0.95; uncorrected machines can be much lower.
Your results
Uses the entered arc voltage for every point on the chart. Real arc voltage rises with current, so treat the result as an estimate and verify with a power meter.
Input power (kW) vs welding current
Sweeps Welding current from 100 to 500, holding your other inputs fixed.
Job costing with real energy data
Tell us how utilities are allocated to work orders and we will suggest a practical approach.
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How to use it
Enter the typical arc voltage and welding current, the efficiency and power factor of the machine from its data sheet, and your supply voltage. Add arc-on hours per month and your tariff. The calculator returns arc power, input kW and kVA, per-phase supply current and the energy cost for welding. Use the supply current to check cable and breaker size, and kVA to size a generator with sensible margin.
The formulas
Arc power in kW is volts times amps divided by 1000. Input power is arc power divided by efficiency. Apparent power in kVA is input power divided by power factor. Three-phase line current equals kVA times 1000 divided by the square root of three times line voltage. For example, 28 V at 300 A with 85 percent efficiency and 0.9 power factor draws about 9.9 kW, 11 kVA and roughly 15 A per phase at 415 V.
Interpreting the result
The cost shown covers energy while the arc is on. Idle draw from fans, controls and wire feeders adds a smaller but constant load, which matters in shops with many machines left powered all day. Compare against gas and wire costs: electricity is usually the smallest of the three consumables, so efficiency gains pay back mostly through lower supply infrastructure and generator size, not the tariff.
- Use nameplate input current as a cross-check
- Add margin for generator starting surges
- Review power factor if utility penalties apply
Common mistakes
Using welding current as if it were supply current is the classic error. The machine draws far less current from the mains than it delivers to the arc, because output voltage is low. Another is ignoring duty cycle: sizing for 100 percent when the real duty is 40 percent wastes capital, while ignoring peak demand can trip a breaker.
Frequently Asked Questions
How many kW does a 300 A welder use?
At 28 V arc voltage, arc output is about 8.4 kW. With 85 percent efficiency the input is around 9.9 kW. Real draw varies with voltage, process and machine design, so measure if cost matters.
How do I size a generator for a welder?
Use input kVA at the highest current you will weld at, then add margin, commonly 25 to 50 percent, for starting surges and other loads. Check the machine manual for minimum generator guidance.
Why is supply current so much lower than welding current?
Arc voltage is low, about 20 to 35 V, while supply voltage is hundreds of volts. Power is roughly conserved, so current on the supply side is a small fraction of weld current.
Does power factor change my electricity bill?
Residential and many small industrial tariffs bill kWh only, but larger consumers may pay for kVA demand or low power factor penalties. It always affects cable and generator sizing.
If energy per job matters for quoting, Netray can help bring metered consumption into your ERP costing, running on your own infrastructure.
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