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Carbon Equivalent Calculator

You can determine the equivalent carbon content in steel using this carbon equivalent calculator.

Clear
Carbon equivalent (IIW)0.43733moderate — preheat for thick sections
Weldabilitymoderate — preheat for thick sections
Suggested minimum preheat100 °F38 °C — increase with thickness
AWS D1.1 formula0.48733includes silicon in the manganese term
Ito–Bessyo Pcm0.27283better suited to low-carbon microalloyed steels
Carbon contribution0.1841.2% of the total
Manganese contribution0.2
Cr + Mo + V contribution0.034
Ni + Cu contribution0.02333
Total alloy content2.2%

The formula

CE = C + Mn ÷ 6 + (Cr + Mo + V) ÷ 5 + (Ni + Cu) ÷ 15

One number for hardenability

The carbon equivalent rolls a steel’s alloy content into a single figure expressing how much like plain carbon steel it behaves when welded. Carbon dominates, and the divisors weight each other element by how much less it contributes.

What it predicts is the risk of a hard, brittle martensitic zone forming beside the weld as it cools, and with it hydrogen cracking. Preheating slows the cooling and gives hydrogen time to diffuse out, which is why the preheat requirement rises with CE.

Above about 0.45 you should be following a proper welding procedure rather than a rule of thumb — thickness, restraint, electrode hydrogen level and interpass temperature all matter as much as the chemistry.