Welding Heat Input Calculator (kJ/mm)
Estimate weld heat input from voltage, amperage, travel speed, and thermal efficiency in metric or imperial speed units.
- Enter electrical settings Input arc voltage and amperage measured during the weld pass.
- Enter travel speed and units Set travel speed and choose whether the value is in mm/min or in/min so the calculator can normalize to kJ/mm.
- Select process efficiency Choose a process preset (MIG/TIG/SMAW) or enter a custom thermal efficiency factor.
- Calculate heat input Press Calculate to return heat input in kJ/mm and converted kJ/in.
What is the welding heat-input formula?
A standard estimate is H(kJ/mm) = ((V × I × 60) / (S × 1000)) × η, where V is voltage, I is amperage, S is travel speed in mm/min, and η is thermal efficiency. The calculator converts in/min to mm/min automatically when needed.
Why does travel speed change heat input so much?
Heat input is inversely proportional to travel speed. Slower travel puts more energy into each millimeter of weld, raising heat input, while faster travel lowers energy per unit length.
Can this replace WPS/PQR requirements?
No. This is a planning and QA estimate. Production welding still requires qualified procedures and compliance with project code/specification limits for heat input, interpass temperature, and metallurgy controls.