Welding Heat Input Calculator
Heat input in kJ/mm from voltage, current and travel speed, with EN 1011 process efficiency factors — for WPS and CE-marked work.
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Heat Input per EN 1011
Q = k × (U × I × 60) ÷ (v × 1000) — voltage × current × 60, divided by travel speed in mm/min, times the process efficiency factor k: 1.0 for submerged arc, 0.8 for MMA/stick and MIG/MAG, 0.6 for TIG (EN 1011-1). Example: 24 V, 150 A MIG at 200 mm/min gives 0.8 × 1.08 = 0.86 kJ/mm.
Why it matters: too much heat input coarsens the grain and weakens impact toughness (critical on fine-grained and quenched steels); too little risks hardening and hydrogen cracking. WPS documents state an allowed range — this calculator tells you where your parameters land. American practice (AWS) uses kJ/in without the k factor; multiply kJ/mm by 25.4 to compare.
Frequently Asked Questions
How do I measure travel speed?
Time a measured weld length: 300 mm covered in 90 seconds = 200 mm/min. On mechanized rigs read it from the carriage setting.
Why does TIG get 0.6 while submerged arc gets 1.0?
The factor is arc efficiency — how much arc energy actually enters the plate. An open TIG arc loses ~40% to radiation and the surroundings; a submerged arc burns under flux with almost no loss.
What is a typical acceptable range?
Structural steel commonly runs 1.0-2.5 kJ/mm; fine-grained/high-strength steels are often capped near 1.5 and may also have a minimum via preheat requirements. The WPS or application standard governs.
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Welding Heat Input Calculator