Welding Heat Input Calculator
Enter arc voltage, current and travel speed to find welding heat input in kJ/mm and kJ/in. Pick the arc efficiency factor that matches your process to match procedure (WPS) limits.
How to calculate welding heat input
- Enter the arc voltage in volts and the welding current in amperes.
- Enter the travel speed in millimetres per minute.
- Choose the arc efficiency for your process, then read the heat input in kJ/mm and kJ/in.
Examples
GMAW pass
24 V, 200 A, 300 mm/min, efficiency 0.8
0.768 kJ/mm (19.51 kJ/in)
Higher current pass
28 V, 250 A, 250 mm/min, efficiency 0.8
1.344 kJ/mm (34.14 kJ/in)
Frequently asked questions
What is the welding heat input formula?
Heat input (kJ/mm) = (volts x amps x 60) / (travel speed in mm/min x 1000) x efficiency. The 60 converts watts to joules per minute and the 1000 converts to kilojoules. This part is an exact formula.
What arc efficiency should I use?
Common transfer factors are about 1.0 for submerged arc (SAW), 0.8 for stick (SMAW) and MIG/MAG (GMAW), and 0.6 for TIG (GTAW). These are documented rules of thumb from AWS and EN 1011-1; always follow your procedure if it states a value.
Why does heat input matter?
Heat input affects cooling rate, hardness, distortion and toughness. Welding procedures (WPS) often set a maximum, and sometimes a minimum, heat input to keep the weld inside qualified limits.
How do I convert kJ/mm to kJ/in?
Multiply kJ/mm by 25.4, since there are 25.4 millimetres in an inch. This conversion is exact, so 1 kJ/mm equals 25.4 kJ/in.
Does this assume a single straight pass?
Yes. It treats travel speed as constant along a straight bead. For weaving, the effective travel speed is lower, which raises heat input, so measure the actual speed over the weld length.
Related tools
Weld Metal Volume Calculator
Calculate filler weld metal volume and weight for a groove weld from cross section area, length and metal density, in grams and pounds.
Welding Amperage Calculator
Estimate stick (SMAW) welding amperage from electrode diameter using the 1 amp per 0.001 inch rule of thumb, with a practical amp range.
Welding Cost Calculator
Estimate total welding cost from filler metal, labor, gas and power. Add deposition efficiency to size electrode purchased versus deposited.
Shielding Gas Calculator
Calculate MIG and TIG shielding gas used from flow rate and weld time, plus how long a gas cylinder lasts at a given CFH flow rate.
Welding Rod Consumption Calculator
Estimate how many stick welding rods a job needs from weld metal weight, SMAW deposition efficiency and rod weight, with electrode pounds.