This free welding heat input calculator turns arc voltage, welding current and travel speed into heat input in kJ/mm or kJ/in. It follows the ASME Section IX and AWS method (no efficiency factor) and the EN 1011-1 method (with a process thermal efficiency factor k), so you can see both numbers side by side. You can also solve for the travel speed that gives a target heat input, check the result against a WPS limit, and download a PDF or Word report.
ASME Section IX / AWS method and EN 1011-1 method. Metric and imperial.
Results
For estimating and learning only. This tool applies the arc-energy formula; it does not check preheat, interpass temperature, cooling rate, joint thickness, procedure qualification or whether a limit applies to your steel. Use the heat input range on your qualified WPS and verify with a qualified welding engineer.
How to Use the Welding Heat Input Calculator
- Choose Metric or Imperial units. Values already typed are converted for you.
- Pick the method. Use ASME / AWS when your procedure follows ASME Section IX or AWS D1.1 (no efficiency factor). Use EN 1011-1 when your procedure follows the European method, then select the welding process so the correct k factor is applied.
- Enter the arc voltage and welding current read from the power source or the WPS.
- Enter the travel speed. If you only know the weld length and the arc time, divide length by time first.
- To work backwards, switch Solve for to travel speed and enter the heat input you need to stay under.
- Optionally enter the maximum heat input from your WPS to get a pass or fail line, then download the PDF or Word report.
Welding Heat Input Formula
Heat input is the electrical energy delivered to the weld for each unit length of weld. In kJ/mm, with travel speed in mm/min:
Heat input (kJ/mm) = k × V × I × 60 / (S × 1000)
Here V is arc voltage in volts, I is welding current in amps, S is travel speed in mm/min and k is the thermal efficiency factor. For the ASME Section IX and AWS method, k is taken as 1, and the same formula in inches gives J/in:
Heat input (J/in) = V × I × 60 / S (S in in/min)
Divide by 1000 for kJ/in. To convert between units, 1 kJ/in = 0.03937 kJ/mm, or 1 kJ/mm = 25.4 kJ/in.
Thermal Efficiency Factors by Process
The EN 1011-1 method multiplies arc energy by a factor k that depends on the welding process. The values below are the commonly published factors; confirm them against the edition of the standard named in your procedure.
| Welding Process | Typical k Factor |
|---|---|
| Submerged arc welding (SAW) | 1.0 |
| Manual metal arc (MMA / SMAW) | 0.8 |
| MIG / MAG / flux-cored (FCAW) | 0.8 |
| TIG (GTAW) | 0.6 |
| Plasma | 0.6 |
Worked Examples
The table shows the calculator output for four typical settings, so you can check your own numbers against them.
| Process | Volts | Amps | Travel Speed | Arc Energy | EN 1011-1 Heat Input |
|---|---|---|---|---|---|
| MMA | 23 | 120 | 150 mm/min | 1.104 kJ/mm | 0.883 kJ/mm |
| MAG | 24 | 220 | 300 mm/min | 1.056 kJ/mm | 0.845 kJ/mm |
| TIG | 12 | 150 | 100 mm/min | 1.080 kJ/mm | 0.648 kJ/mm |
| SAW | 30 | 600 | 500 mm/min | 2.160 kJ/mm | 2.160 kJ/mm |
kJ/mm to kJ/in Conversion Table
Use this table to move a heat input limit between metric and imperial procedures.
| kJ/mm | kJ/in |
|---|---|
| 0.5 | 12.7 |
| 1.0 | 25.4 |
| 1.5 | 38.1 |
| 2.0 | 50.8 |
| 2.5 | 63.5 |
| 3.0 | 76.2 |
Frequently Asked Questions
What Is Welding Heat Input?
Heat input is the electrical energy supplied to the weld per unit length, found by dividing arc power (volts times amps) by travel speed. It is reported in kJ/mm or kJ/in. It influences how fast the weld and the surrounding metal cool, which in turn affects the heat-affected zone and the properties of the joint.
How Do You Calculate Heat Input in kJ/mm?
Multiply voltage by current, multiply by 60, then divide by travel speed in mm/min times 1000. For example, 24 V at 220 A travelling at 300 mm/min gives 24 × 220 × 60 / (300 × 1000) = 1.056 kJ/mm of arc energy.
What Is the Difference Between Arc Energy and Heat Input?
Arc energy is the raw electrical value, V × I / speed. Heat input under the European method is arc energy multiplied by the thermal efficiency factor k for the process. Under ASME Section IX and AWS, k is taken as 1, so the two terms give the same number. This calculator shows both so you can see which one you are comparing.
Why Do EN 1011-1 and ASME Give Different Answers?
The EN method applies a k factor below 1 for most arc processes, while the ASME and AWS method applies none. The same settings therefore give a lower heat input under EN 1011-1. Always use the method written in your qualified WPS and do not compare values from the two methods directly.
How Do I Measure Travel Speed?
Mark a known bead length, time the arc from start to finish with a stopwatch, and divide length by time. Convert the result to mm/min or in/min before entering it. Measure over a long enough run that starts and stops do not distort the average.
Is There a Maximum Heat Input I Must Stay Under?
Limits come from your qualified welding procedure, the steel producer or the governing code for your project, so they differ from job to job. Enter the maximum from your WPS in the optional field and the calculator will tell you whether the result is within it. This tool does not set limits for you.
Sources and References
- ASME Boiler and Pressure Vessel Code, Section IX, Welding, Brazing, and Fusing Qualifications, QW-409.1 Heat Input — American Society of Mechanical Engineers (paid standard).
- AWS D1.1/D1.1M, Structural Welding Code – Steel, heat input provisions — American Welding Society (paid standard).
- EN 1011-1, Welding – Recommendations for welding of metallic materials – Part 1: General guidance for arc welding, thermal efficiency factor k — European Committee for Standardization (paid standard).
Check the edition and clause numbers in the copy of each standard your project specifies, as requirements are revised between editions.
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