Welding Heat Input Calculator
Calculate welding heat input (kJ/mm) from voltage, current, and travel speed, corrected for process thermal efficiency.
Results
What is it?
Welding heat input quantifies the energy delivered per unit length of weld. It is a critical parameter in weld procedure specifications (WPS) because it controls the size and cooling rate of the heat-affected zone (HAZ). High heat input causes grain growth, distortion, and loss of toughness in the HAZ; too low causes lack of fusion and rapid quench hardening in hardenable steels.
How to use
Enter the arc voltage, welding current, and travel speed from your welding parameters. Select the welding process to apply the appropriate thermal efficiency factor (fraction of electrical energy that enters the weld). The net heat input reflects actual energy delivered to the weld.
Example scenario
GMAW at 24 V, 200 A, 400 mm/min. Gross HI = (24 × 200 × 60) / 400 / 1000 = 0.72 kJ/mm. Net HI = 0.72 × 0.85 = 0.61 kJ/mm. Most structural codes limit heat input to 3.5–5 kJ/mm for high-strength steels to prevent HAZ softening.
Pro tip
Preheat requirements increase with heat input and carbon equivalent of the base metal. Higher heat input on quenched and tempered (QT) steels can wipe out the tempering — observe the maximum interpass temperature. SAW has η = 1.00 because submerged arc flux captures nearly all arc energy into the joint.