How do you calculate weld heat input?

Divide arc power (volts times amps) by travel speed in in/min, then multiply by a factor that includes process efficiency and unit conversion. Here 5280 W / 15 in/min gives 352, times 0.048 yields 16.9 kJ/in.

What is the process efficiency factor in this calculation?

It is the arc transfer efficiency (how much arc energy enters the weld) combined with the unit conversion from watt-minutes per inch to kJ/in. The 0.048 default bundles a typical efficiency with that conversion; flux-cored and MIG sit around 0.8 efficiency, TIG lower.

What is a good weld heat input?

It is governed by the WPS and base metal, not a universal ideal. Carbon steel often tolerates 15-50 kJ/in; quenched-and-tempered and high-strength low-alloy steels cap lower to protect properties. The 16.9 kJ/in result is a moderate value for many structural procedures.

How does travel speed affect heat input?

Inversely — heat input is divided by travel speed, so welding faster lowers it. Doubling travel speed from 15 to 30 in/min at the same arc power would halve heat input to about 8.4 kJ/in.

Why does high heat input cause problems?

It slows cooling, which coarsens grain in the heat-affected zone, lowers toughness, and increases distortion. On Q&T steels it can temper-soften the base metal below spec strength.

Heat input vs arc energy — what's the difference?

Arc energy is the raw volts-times-amps over travel speed (352 here in raw units). Heat input is arc energy multiplied by the process efficiency factor, since not all arc energy enters the weld — giving the effective 16.9 kJ/in.

Welding & Fabrication calculator

Weld Heat Input Calculator

Weld heat input is the thermal energy delivered per unit length of weld, the master variable behind cooling rate, distortion, and the size of the heat-affected zone. Welding engineers and CWIs use it to write and qualify procedures (WPS/PQR), because too much heat softens quenched-and-tempered steels and too little risks hydrogen cracking. It is calculated from arc power divided by travel speed, scaled by a process efficiency factor that also converts the units. On the floor, it is the number an inspector checks when a code calls out a heat input range you must stay inside.

What this calculator does

Estimate weld heat input from arc power (volts x amps) and travel speed, with a process efficiency factor.
Use it for a quick check on heat input for HAZ control, distortion management, or staying inside the WPS heat input window.
It divides arc power by travel speed to get raw energy per inch, then multiplies by a process efficiency factor that both accounts for arc losses and converts watt-minutes per inch into kilojoules per inch.

Formula used

Raw heat input per inch = arc power (volts x amps) ÷ weld travel speed
Effective weld heat input = raw heat input per inch × process efficiency factor

Inputs explained

Arc power (volts x amps): Multiply welding volts by amps. Example: 24 V x 220 A = 5280 W. Use WPS values or as measured at the arc.
Weld travel speed: From the WPS or a stopwatch on the booth. Heat input rises as travel speed slows.
Process efficiency factor (kJ basis): Use 0.048 for GMAW/FCAW (0.8 efficiency x 0.06 unit factor), 0.036 for GTAW, 0.057 for SAW to return kJ/in.

How to use the result

Use it when qualifying a welding procedure, verifying production welds against a code-specified heat input window, or diagnosing distortion and HAZ problems.
It treats arc power as steady volts times amps; pulsed or waveform-controlled processes need instantaneous power integration, and the efficiency factor must match the actual process.

Current U.S. benchmarks

The producer price index for steel mill products stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Industrial electricity averages 8.66 cents per kWh across the U.S. (EIA, Apr 2026), up 5.5% from a year earlier. Energy-intensive steps carry this directly into unit cost.
U.S. iron and steel imports ran $2.1B in May 2026 (Census International Trade). The U.S. ran a trade deficit of $0.4B in the category that month. Import volumes are the pressure gauge behind tariff and reshoring decisions.
The U.S. has 53,790 fabricated metal products establishments employing about 1,441,471 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate weld heat input? Divide arc power (volts times amps) by travel speed in in/min, then multiply by a factor that includes process efficiency and unit conversion. Here 5280 W / 15 in/min gives 352, times 0.048 yields 16.9 kJ/in.
What is the process efficiency factor in this calculation? It is the arc transfer efficiency (how much arc energy enters the weld) combined with the unit conversion from watt-minutes per inch to kJ/in. The 0.048 default bundles a typical efficiency with that conversion; flux-cored and MIG sit around 0.8 efficiency, TIG lower.
What is a good weld heat input? It is governed by the WPS and base metal, not a universal ideal. Carbon steel often tolerates 15-50 kJ/in; quenched-and-tempered and high-strength low-alloy steels cap lower to protect properties. The 16.9 kJ/in result is a moderate value for many structural procedures.
How does travel speed affect heat input? Inversely — heat input is divided by travel speed, so welding faster lowers it. Doubling travel speed from 15 to 30 in/min at the same arc power would halve heat input to about 8.4 kJ/in.
Why does high heat input cause problems? It slows cooling, which coarsens grain in the heat-affected zone, lowers toughness, and increases distortion. On Q&T steels it can temper-soften the base metal below spec strength.

Last reviewed 2026-05-12.