# Carbon Equivalent Calculator

URL: https://speedycalculator.com/calculators/construction/carbon-equivalent/
Last updated: 2026-10-25

> The carbon equivalent calculator works out the weldability of steel from its chemical composition using the IIW carbon equivalent, the AWS D1.1 formula and the Ito–Bessyo Pcm for low-carbon steels.

## Inputs

- Carbon C (%)
- Manganese Mn (%)
- Silicon Si (%)
- Chromium Cr (%)
- Molybdenum Mo (%)
- Vanadium V (%)
- Nickel Ni (%)
- Copper Cu (%)
- Boron B (%)

## Results

- CE (IIW)
- CE (AWS D1.1)
- Pcm (Ito–Bessyo)

## Formula

```
CE (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
CE (AWS D1.1) = C + (Mn + Si)/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
Pcm = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B
```

## Explanation

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)

CEWeldability≤ 0.35Excellent0.36–0.40Very good0.41–0.45Good – pre-heat thick sections0.46–0.50Fair – pre-heat and low-hydrogen> 0.50Poor – 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

FieldWhat to enterCarbon CIn %Manganese MnIn %Silicon SiIn %Chromium CrIn %Molybdenum MoIn %Vanadium VIn %Nickel NiIn %Copper CuIn %Boron BIn %

### 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]

## Worked 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 %.

## FAQ

**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.


## Sources

- [AWS D1.1 Structural Welding Code – Steel, Annex H](https://www.aws.org/)