Welding heat input calculator
Calculate arc energy and heat input in kJ/mm from welding voltage, current and travel speed. The thermal efficiency factor k is applied for the welding process as defined in EN 1011-1, so the result can be compared directly with the heat input limits on a WPS.
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What it calculates
- Arc energy E in kJ/mm
- Heat input Q = k × E for the selected process
- Thermal efficiency k: 0.8 for MIG/MAG (131/135/136/138), SMAW (111) and FCAW, 0.6 for TIG (141) and plasma (15), 1.0 for submerged arc (121)
- Travel speed in mm/min, with imperial units available
Formulas
E = U × I × 60 / (v × 1000) [kJ/mm, U in V, I in A, v in mm/min] Q = k × E
Worked example
25 V, 220 A and 300 mm/min give E = 25 × 220 × 60 / (300 × 1000) = 1.10 kJ/mm. With MAG welding (k = 0.8) the heat input is Q = 0.88 kJ/mm.
How to use it
- Create a free account with Google or e-mail.
- Open the calculator and enter your values; units can be metric or imperial.
- Read the result with its formula and source, and export to PDF, DXF or CSV where available.
Free account with Google or e-mail
Frequently asked questions
What is the difference between arc energy and heat input?
Arc energy is the electrical energy per unit length of weld. Heat input is the part of it that actually enters the workpiece: arc energy multiplied by the thermal efficiency factor k of the process (EN 1011-1).
Which heat input is allowed for high-strength steels?
It depends on the steel and the plate thickness. Quenched and tempered and TMCP steels such as S690QL, Hardox and Strenx have a heat input window from the steel maker; the Heat input check tool in BenchMaths compares each run against that window together with the t8/5 cooling time.
Is the calculator free?
Yes. Creating an account is free, with Google or e-mail.
Guides
- S355 preheat temperature by thicknessS355 needs no preheat in thin plate, but from around 10–15 mm upwards a minimum preheat is required to avoid hydrogen cracking.
- How to calculate welding heat inputHeat input is the energy that enters the workpiece per millimetre of weld.
- WPS vs PQR (WPQR)A WPS tells the welder how to make a weld.
Related calculators
- Preheat temperature calculatorPick a material and plate thickness to get the minimum preheat temperature.
- Filler metal and shielding gas selectorSelect the two base metals and the welding process.
- Weld metal and consumables calculatorEnter the joint type, dimensions and weld length.
- Heat input check and t8/5 cooling timeChoose the two base metals, process and filler, then enter preheat and the welding parameters for each run.
Results are engineering estimates for planning. They do not replace the applicable standard, a qualified procedure or a check by a qualified engineer.