Heat Input Calculator
Calculate heat input for any welding method. Results compliant with EN ISO standards.
What is heat input?
Heat input includes the thermal efficiency factor k. It is not the same as arc energy, which is calculated without that efficiency factor.
- Q – heat input [kJ/mm]
- k – thermal efficiency factor (0.6–1.0 to EN 1011-1)
- U – arc voltage [V]
- I – welding current [A]
- v – welding speed [mm/s]
Working in imperial units? Switch the calculator to kJ/in — 1 kJ/mm = 25.4 kJ/in, travel speed is entered in in/min (ipm), and the formula becomes Q = (k × U × I × 60) / (v × 1000).
🔥 Heat Input Calculator
Calculates heat input with thermal efficiency or arc energy without the efficiency factor. You can enter single values or ranges (e.g., 100-120).
Why is heat input important?
Mechanical properties
Excessive heat input can cause grain growth and reduced toughness in the HAZ.
Hydrogen cracking
Heat input control is crucial for preventing cold cracking in fine-grained and high-strength steels.
Standards requirements
Standards such as EN ISO 15614 require documenting heat input in WPQR.
Repeatability
Consistent heat input ensures repeatability of welded joint properties.
Frequently asked questions
The heat input formula is: Q = (k × U × I) / (v × 1000), where k is the thermal efficiency factor, U is arc voltage [V], I is welding current [A], and v is travel speed [mm/s]. With travel speed in in/min the same formula reads Q = (k × U × I × 60) / (v × 1000) and the result comes out in kJ/in. Arc energy is calculated without k.
Heat input is expressed in kilojoules per millimetre [kJ/mm] under EN ISO practice and in kilojoules per inch [kJ/in] under AWS practice; kJ/cm and J/mm are also used. The conversion is 1 kJ/mm = 25.4 kJ/in, and this calculator switches between both.
Thermal efficiency factors to EN 1011-1: MAG (GMAW) = 0.8; TIG (GTAW) = 0.6; MMA (SMAW) = 0.8; SAW = 1.0; plasma = 0.6. The standard gives them as conventional values to be used in the calculation.
Heat input directly affects the mechanical properties of the weld, the size of the heat-affected zone (HAZ), susceptibility to cold cracking, and cooling rate. Too high heat input can cause grain growth and reduced impact strength.
Yes, standard EN ISO 15614-1 requires documenting heat input in the Welding Procedure Qualification Record (WPQR). It is one of the key qualification parameters.
For fine-grained and high-strength steels, controlled lower heat input (typically 0.5-1.5 kJ/mm) is recommended to maintain strength parameters and impact toughness in the heat-affected zone (HAZ).
That number belongs on a WPS
WeldStack's WPS builder computes heat input automatically from the pass parameters, keeps it inside the procedure document, and exports audit-ready PDFs — with welder qualifications and WPQR records in the same system. Free trial, no credit card.