Welding Heat Input Calculator

Calculate arc welding heat input from voltage, amperage, travel speed and process efficiency. Returns kJ/mm, kJ/in, arc power and J/mm for WPS and procedure screening.

Inputs

View results

Arc voltage (V)

Measured or procedure arc voltage.

Welding current (I)

Measured or procedure welding current.

Travel speed (S)

Torch or electrode travel speed along the weld.

mm/min

Process efficiency (eta)

Arc efficiency or heat-transfer efficiency used by your procedure basis.

Results

Default result

Edit inputs

Heat input(H)

0.6912kJ/mm

H = V * I * 60 * efficiency / (1000 * travel speed).

Also computed

Heat input(H)17.56kJ/in

Energy per length691.2J/mm

Arc power(P)4.32kW

Travel speed used(S)300mm/min

Efficiency used(eta)0.8

Method notes 3 notes

Use measured average current, voltage and travel speed when comparing a real weld to a procedure heat-input range.
Process efficiency is procedure-dependent. Keep the same efficiency convention when comparing against WPS, code or project limits.
This does not evaluate weld size, throat, preheat, interpass temperature, cooling rate, toughness, hydrogen control or metallurgy.

Welding heat input is H = V·I·60·η/(1000·S), where V is arc voltage, I is current, η is process efficiency and S is travel speed in mm/min. The result is kJ/mm, with kJ/in shown by multiplying by 25.4. Use it to compare measured or planned weld parameters with a WPS heat-input range.

How to use this calculator

Enter voltage and current. Use measured average arc voltage and welding current when checking a real weld.
Enter travel speed. Use the torch/electrode speed along the weld bead.
Enter efficiency. Use the efficiency factor required by your procedure or comparison basis.
Read heat input. Compare kJ/mm or kJ/in with your allowed procedure range.

How it works

Arc power is voltage times current:

P = V x I

Heat input divides that power by travel speed, with a process efficiency factor:

H = V x I x 60 x eta / (1000 x S)

When S is in mm/min, H is in kJ/mm. The calculator also multiplies by 25.4 to show kJ/in.

Worked example

Verified against the live calculator

With 24 V, 180 A, 300 mm/min travel speed and 80% efficiency, arc power is 4.32 kW. Heat input is 24 x 180 x 60 x 0.80 / (1000 x 300), or 0.691 kJ/mm. That is 17.6 kJ/in.

Frequently asked questions

How do you calculate welding heat input?

Use H = V x I x 60 x efficiency / (1000 x travel speed). With voltage in volts, current in amps and travel speed in mm/min, the result is kJ/mm.

Why is travel speed in the denominator?

The arc power is energy per second. Slower travel spends more time over each millimetre of weld, so the heat input per length rises.

What efficiency should I use?

Use the efficiency convention required by your WPS, code, customer or procedure basis. The calculator does not prescribe a process efficiency because different standards and processes use different assumptions.

Does heat input prove a weld is acceptable?

No. Heat input is one procedure variable. Weld size, throat, joint detail, preheat, interpass temperature, filler, base metal, hydrogen control, inspection and qualification still matter.

Method & assumptions

Uses average voltage, current and travel speed for a straight heat-input calculation.
Efficiency is user-entered so the same calculator can match the convention in the governing WPS, code or customer requirement.
Does not evaluate weld throat, weld-group stress, base metal, preheat, interpass temperature, hydrogen, toughness or inspection acceptance.
Use the weld throat calculator, fillet weld size calculator and weld group calculator for weld sizing checks.

Welding Heat Input Calculator

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