Heat input calculator
Arc energy for a weld run, by the ISO method (with a thermal efficiency factor) or the ASME IX method (without one). Example values are filled in so you can see how it works.
Inputs
The working
- Arc energy
U x I x 60 / v1,920 J/mm - Heat input, ISO method
Q = k x (U x I x 60 / v) / 10001.536 kJ/mm
For guidance only. Verify against the code edition in force and your own design basis.
This heat input calculator gives welding heat input in kJ/mm, kJ/in and J/mm from voltage, current and travel speed, by the ISO or ASME IX method. Free, no sign-up.
The formula
- Arc energy (J/mm) = volts x amps x 60 / travel speed (mm/min).
- ISO: heat input (kJ/mm) = k x volts x amps x 60 / (travel speed x 1000).
- ASME IX: no k. kJ/mm = J/mm / 1000; J/in = J/mm x 25.4.
- Timed run: travel speed = length (mm) / time (s) x 60.
Worked example
Limits
Common questions
How do I calculate heat input for welding?
Multiply arc voltage by welding current, multiply by 60 and divide by travel speed in mm/min to get J/mm. Divide by 1,000 for kJ/mm, and for the ISO method multiply by the thermal efficiency factor k first. For example, 24 V, 200 A and 150 mm/min give 1,920 J/mm, which is 1.536 kJ/mm with k = 0.8.
What is the difference between the ISO and ASME IX methods?
The ISO method applies a thermal efficiency factor k, so for most processes it gives a lower figure than ASME IX, which applies none. The same weld gives 1.536 kJ/mm by ISO (k = 0.8) and 1.92 kJ/mm by ASME IX. Use the method your procedure or standard calls for.
What thermal efficiency factor k should I use?
Use the figure in your welding procedure or the standard it cites. The calculator offers a typical starting value: 1.0 for submerged arc, 0.8 for manual metal arc, MIG / MAG and flux cored, and 0.6 for TIG and plasma. You can overwrite it.
How do I convert heat input from kJ/mm to kJ/in?
Multiply kJ/mm by 25.4, because one inch is 25.4 mm. For example, 1.536 kJ/mm is 39.01 kJ/in. One kJ/mm is also 1,000 J/mm.
Unit conversions
Reference values for the units this tool works in. Rounded for reading; the calculator itself works to full precision.
Heat input
| kJ/mm | kJ/in | J/mm |
|---|---|---|
| 0.5 | 12.7 | 500 |
| 0.8 | 20.32 | 800 |
| 1 | 25.4 | 1,000 |
| 1.2 | 30.48 | 1,200 |
| 1.5 | 38.1 | 1,500 |
| 2 | 50.8 | 2,000 |
| 2.5 | 63.5 | 2,500 |
| 3 | 76.2 | 3,000 |
1 kJ/mm = 25.4 kJ/in = 1000 J/mm.
Travel speed
| mm/min | in/min | mm/s |
|---|---|---|
| 100 | 3.937 | 1.667 |
| 150 | 5.906 | 2.5 |
| 200 | 7.874 | 3.333 |
| 250 | 9.843 | 4.167 |
| 300 | 11.81 | 5 |
| 400 | 15.75 | 6.667 |
| 500 | 19.69 | 8.333 |
1 in/min = 25.4 mm/min.
Length
| mm | in |
|---|---|
| 1.5 | 0.0591 |
| 3 | 0.1181 |
| 5 | 0.1969 |
| 6 | 0.2362 |
| 6.35 | 0.25 |
| 8 | 0.315 |
| 10 | 0.3937 |
| 12.7 | 0.5 |
| 16 | 0.6299 |
| 20 | 0.7874 |
| 25.4 | 1 |
| 50 | 1.969 |
| 100 | 3.937 |
1 in = 25.4 mm.
Where heat input shows up
A procedure's range of heat input is checked on the weld, not on the shelf. In SkaldIQ a monitored weld carries its recorded values against the limits of the procedure it was welded to.
Typical efficiency values
The efficiency factor offered for each process is a typical value you can overwrite. Use the figure your procedure or your standard gives.
Keep the working
In the full system a calculation can be issued as a branded sheet with your name and the date it was run, kept with the project.