Welding Heat Input Calculator

Formula

• Heat input HI = (η × V × I) / travel speed
• HI in kJ/mm when travel speed is mm/min and η is thermal efficiency
• Arc power = V × I / 1000 kW

About this calculator

Part of our Manufacturing Calculators collection. Welding, stamping, punch and die tooling, 3D printing, material weight, and production automation.

How it works

Heat input equals thermal efficiency times voltage times current divided by travel speed. Arc power shows instantaneous welding power. Cooling rate and preheat estimates use plate thickness, material type, and ambient temperature heuristics. Warning flags heat input above typical process limits.

Enter your values in the inputs above and click CALCULATE. Results appear on the right without a page reload. No login and no server upload.

Worked example

SMAW 25 V, 150 A, 300 mm/min travel, η = 0.75.

1. Travel = 300/60 = 5 mm/s
2. HI = 0.75 × 25 × 150 / (5 × 1000) = 0.563 kJ/mm
3. Arc power = 3.75 kW
4. Below SMAW limit 3.5 kJ/mm → Within limit

Result: Heat input 0.56 kJ/mm, within process limit.

When to use

• Checking heat input against WPS limits
• Estimating preheat need from plate thickness
• Comparing processes at same arc energy

Limitations

• Preheat and cooling rate are heuristic, not FEA
• Ambient temperature reduces preheat estimate only
• Process limits are typical, not project-specific

FAQ

What is thermal efficiency η?

Fraction of arc energy deposited in the plate. SMAW ~0.75, GMAW ~0.80, GTAW ~0.60, SAW ~0.95 — use your WPS value.

Why did preheat show zero?

For thin plate at moderate heat input, calculated preheat may round to zero. Increase thickness or lower heat input to see preheat rise.

What triggers Above limit?

Heat input exceeds a typical maximum for the selected process. High heat input can reduce HAZ toughness.