Carbon and alloying elements make steel harder, and a hard heat-affected zone next to a weld can crack as hydrogen escapes. The carbon equivalent collapses the composition into one number that predicts this risk and decides whether pre-heat is needed. Below about 0.40 most steels weld easily; above 0.45–0.50 pre-heating and low-hydrogen processes are usually required.
How to use the Carbon Equivalent Calculator
- Carbon C
- Manganese Mn
- Silicon Si
- Chromium Cr
- Molybdenum Mo
- Vanadium V
- Nickel Ni
- Copper Cu
- Boron B
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the mass percentages from the mill certificate. Elements that are not listed can be left at zero.
Weldability guide (IIW CE)
| CE | Weldability |
|---|---|
| ≤ 0.35 | Excellent |
| 0.36–0.40 | Very good |
| 0.41–0.45 | Good – pre-heat thick sections |
| 0.46–0.50 | Fair – pre-heat and low-hydrogen |
| > 0.50 | Poor – strict procedure required |
Tips for an accurate estimate
- Keep units consistent – the calculator handles conversions, but check every field’s unit before reading a result.
- Use values from standards, data sheets or test pieces whenever you have them; typical values are only a starting point.
- Apply appropriate safety factors and have structural, electrical and pressure work checked by a qualified professional.
- Record the inputs you used so the calculation can be reviewed later.
Common mistakes to avoid
- Confusing diameter and radius, or nominal and actual sizes.
- Using allowable stresses and ultimate strengths interchangeably.
- Treating rule-of-thumb results as a substitute for code tables or an engineered design.
Inputs explained
| Field | What to enter |
|---|---|
| Carbon C | In % |
| Manganese Mn | In % |
| Silicon Si | In % |
| Chromium Cr | In % |
| Molybdenum Mo | In % |
| Vanadium V | In % |
| Nickel Ni | In % |
| Copper Cu | In % |
| Boron B | In % |
What each result means
- CE (IIW) = [Carbon C] + [Manganese Mn]÷6 + ([Chromium Cr] + [Molybdenum Mo] + [Vanadium V])÷5 + ([Nickel Ni] + [Copper Cu])÷15
- CE (AWS D1.1) = [Carbon C] + ([Manganese Mn] + [Silicon Si])÷6 + ([Chromium Cr] + [Molybdenum Mo] + [Vanadium V])÷5 + ([Nickel Ni] + [Copper Cu])÷15
- Pcm (Ito–Bessyo) = [Carbon C] + [Silicon Si]÷30 + ([Manganese Mn] + [Copper Cu] + [Chromium Cr])÷20 + [Nickel Ni]÷60 + [Molybdenum Mo]÷15 + [Vanadium V]÷10 + 5×[Boron B]
Formula
CE (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15CE (AWS D1.1) = C + (Mn + Si)/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5BWorked example
Inputs — Carbon C: 0.18 %; Manganese Mn: 1.2 %; Silicon Si: 0.3 %; Chromium Cr: 0.1 %; Molybdenum Mo: 0.02 %; Vanadium V: 0.01 %; Nickel Ni: 0.1 %; Copper Cu: 0.15 %; Boron B: 0 %.
Results — CE (IIW) = 0.423 %; CE (AWS D1.1) = 0.473 %; Pcm (Ito–Bessyo) = 0.267 %.
Frequently asked questions
What carbon equivalent is weldable?
Up to about 0.40 – excellent weldability; 0.41–0.45 good, pre-heat may help; above 0.45–0.50 pre-heat and low-hydrogen consumables are needed.
When should I use Pcm?
For modern low-carbon (C < 0.12%) micro-alloyed steels, where the IIW formula over-predicts cracking risk.
Where do I find the composition?
On the mill test certificate (MTC) supplied with the steel.
What formula does the Carbon Equivalent Calculator use?
CE (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15.