About Welding Heat Input Calculator
The welding heat input calculator turns the three numbers on your welding machine and stopwatch — arc voltage, welding current, and travel speed — into the heat input that welding procedure specifications limit and heat-affected-zone calculations start from: HI = 60 × V × I ÷ (1000 × travel speed), reported in kJ/in and kJ/mm at the same time. Enter the speed in inches or millimetres per minute; the other unit system is always shown alongside (25.4 kJ/mm-to-kJ/in exact ratio).
For codes that work in arc energy with a process efficiency — the EN 1011 convention — pick the welding process and the tool applies the EN 1011-1 Table 1 thermal efficiency factor k (submerged arc 1.0, stick and wire processes 0.8, TIG 0.6) to give the net heat input. Enter your WPS maximum and the badge tells you whether the pass is compliant, judged at the same two-decimal precision the numbers display at.
How It Works
- Read the arc voltage and welding current off the machine while welding (or from the WPS), and time the travel speed: distance welded divided by arc time, in inches per minute or millimetres per minute — use the unit toggle to match how you measured.
- The tool computes gross heat input — arc energy per length of weld — with the standard formula HI = 60 × V × I / (1000 × S). This is the number AWS D1.1 heat-input limits and most North American WPS maximums are written against; no efficiency factor is applied in "Gross" mode.
- If your specification follows EN 1011 (common in Europe and offshore work), pick the process instead: the heat input there is defined with a thermal efficiency factor k — 1.0 for submerged arc, 0.8 for stick (MMA/SMAW), MIG/MAG (GMAW), and flux-cored processes, 0.6 for TIG — and the tool multiplies the gross arc energy by the verified Table 1 factor.
- To check a pass against a procedure limit, enter the WPS maximum in kJ/in (or kJ/mm in metric mode). The pass/fail badge compares the computed heat input — net if a process factor is selected, gross otherwise — at the displayed two-decimal precision, so the verdict always agrees with the numbers you can see.
- Heat input is one control on cooling rate, not the whole story: preheat, interpass temperature, and thickness set the rest. High heat input softens quenched-and-tempered steels; low heat input speeds cooling and raises hardenability concerns — stay inside the WPS window in both directions.
Worked Example
A GMAW fill pass runs at 25 V and 250 A, and the welder covers 10 inches of joint per minute. Gross heat input = 60 × 25 × 250 / (1000 × 10) = 37.5 kJ/in, which is 37.5 ÷ 25.4 = 1.48 kJ/mm. Against a WPS maximum of 40 kJ/in the pass is compliant. If the job is specified to EN 1011 instead, GMAW carries k = 0.8, so the net heat input is 0.8 × 37.5 = 30.0 kJ/in (1.18 kJ/mm).
Formulas
- Heat input (arc energy)
HI = 60 × V × I / (1000 × S)- Net heat input (EN 1011 convention)
Q = k × HI- Unit relation
HI[kJ/in] = 25.4 × HI[kJ/mm]
Standards & References
- AWS D1.1/D1.1M:2020, Structural Welding Code — Steel, subclause 6.8.5.1 (heat input calculation methods) and 7.7 (heat input control for quenched and tempered steels) — D1.1 heat-input limits are written against gross arc energy
- ISO/TR 18491:2015, Guidelines for measurement of welding energies — arc energy E = U × I × 60 / (v × 1000)
- EN 1011-1:2009, Welding — Recommendations for welding of metallic materials, clause 8.7 Formula (1) and Table 1 thermal efficiency factors (verified against the published standard: process 12 SAW 1.0; 111, 131, 135, 114, 136, 137 all 0.8; 141 TIG 0.6)
Frequently Asked Questions
How do I calculate welding heat input?
Multiply arc voltage by welding current and by 60, then divide by 1000 times the travel speed: HI = 60 × V × I / (1000 × S). With speed in inches per minute the answer is in kJ/in; with mm/min it is kJ/mm. Example: 25 V × 250 A at 10 in/min gives 37.5 kJ/in.
What is the difference between heat input and arc energy?
Arc energy is the electrical energy delivered per length of weld — the raw 60·V·I/(1000·S) number. Heat input in the EN 1011 sense multiplies that by a process thermal efficiency k (1.0 submerged arc, 0.8 stick/MIG/MAG/flux-cored, 0.6 TIG) to estimate what actually enters the plate. AWS D1.1 uses the gross arc energy directly and calls it heat input — check which convention your specification follows before comparing numbers.
Why does TIG have a lower efficiency factor than submerged arc?
A submerged arc is buried under flux, so nearly all the arc energy ends up in the joint — EN 1011-1 rates it k = 1.0. An open TIG arc radiates and convects a large share of its energy to the surroundings, so only about 60% reaches the plate (k = 0.6). Open-arc consumable processes (SMAW, MIG/MAG, flux-cored) sit between at 0.8.
Why do WPS documents set a maximum heat input?
High heat input slows cooling, coarsens grain in the heat-affected zone, and drops toughness — and it can soften quenched-and-tempered steels below their specified strength, which is why AWS D1.1 clause 7.7 requires heat input control for them. Many WPSs also carry a minimum, because too-fast cooling raises HAZ hardness and hydrogen-cracking risk. The qualified range comes from the procedure qualification record.
How do I measure travel speed for the calculation?
Measure the length of weld deposited and divide by the arc-on time for that length — a rule and a stopwatch are enough for manual welding. For weave passes use the advance along the joint, not the path of the electrode tip. Modern waveform power sources log volts, amps, and time directly; D1.1:2020 explicitly recognizes those instantaneous-energy methods.
Does this calculator work for pulsed or waveform-controlled welding?
The V × I formula assumes steady values, and average meter readings can misstate the true energy of a pulsed waveform. For waveform-controlled processes, AWS D1.1 and ISO/TR 18491 point to instantaneous energy or power measured by the power source; use the machine's logged joules per length where available and this calculator for conventional (non-pulsed) passes.