Carbon Equivalent Calculator (CE IIW, AWS, Pcm for steel weldability)

Understanding the carbon equivalent calculator — concept and principle

The carbon equivalent (CE) rolls the hardening effect of each alloying element in a steel into one number comparable with carbon. Welding engineers use it as a guide to hardenability and to the risk of hydrogen (cold) cracking in the heat-affected zone, and to decide on preheat.

Alloying elements are converted into “equivalent carbon”; 0.18 + 0.233 + 0.03 + 0.017 ≈ 0.46.

How it is calculated

CE (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15.
CE (AWS D1.1 version) = CE (IIW) + Si/6.
Pcm (Ito–Bessyo) = C + Si/30 + (Mn + Cu + Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B, preferred for modern low-carbon steels (C up to about 0.11%).
All inputs are in weight per cent from the heat analysis.

The principle

When steel cools quickly after welding, carbon and alloying elements promote hard, brittle microstructures such as martensite. Combined with hydrogen from the welding process and residual stress, these can crack hours after welding. Each element's effect is weighted relative to carbon, so the CE gives one number for crack susceptibility. Higher values usually call for preheat, low-hydrogen consumables or controlled cooling.

Worked example

Default inputs: C 0.18, Mn 1.40, Si 0.30, Cr 0.10, Mo 0.03, V 0.02, Ni 0.10, Cu 0.15, B 0 (wt %).

CE (IIW) = 0.18 + 1.40/6 + (0.10 + 0.03 + 0.02)/5 + (0.10 + 0.15)/15 = 0.18 + 0.233 + 0.030 + 0.017 ≈ 0.46.
CE (AWS) = 0.46 + 0.30/6 ≈ 0.51.
Pcm = 0.18 + 0.010 + 1.65/20 + 0.10/60 + 0.03/15 + 0.02/10 ≈ 0.278.
With carbon at 0.18% (above 0.11%), the suitable formula family is IIW or AWS.

Each point is the calculator re-run with only “Manganese Mn (wt %)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Manganese Mn (wt %)	Carbon equivalent CE (IIW)
0.35	0.285
0.7	0.343
1.05	0.402
1.4	0.46
1.75	0.518
2.1	0.577
2.8	0.693

How to read the result

Where does your result fall?

As a rough guide used in practice, steels with a CE (IIW) below about 0.40 are generally considered readily weldable, while higher values need more care; actual preheat depends on thickness, hydrogen level, heat input and the governing code. For this steel, 0.46 suggests that preheat may be needed depending on thickness and consumables.

Common mistakes

Using a specification maximum instead of the actual mill certificate values.
Applying the IIW formula to very low-carbon microalloyed steels, where Pcm fits better.
Comparing values from different formulas as if they were on the same scale.
Ignoring plate thickness and hydrogen level when deciding preheat.

Keep in mind: Carbon equivalent is only a guide. Welding procedures must follow the applicable code (for example AWS D1.1 or EN 1011-2) and be approved by a qualified welding engineer.

Frequently asked questions

What is a good carbon equivalent for welding?

Lower is easier; values below about 0.40 (IIW) are often regarded as readily weldable, depending on thickness and conditions.

What is the difference between CE and Pcm?

CE (IIW) suits conventional carbon steels; Pcm was developed for low-carbon steels and weighs carbon more strongly.

Why does manganese count less than carbon?

Each element's hardening effect per per cent is smaller than carbon's, so it is divided by a factor.

Sources: International Institute of Welding (IIW), carbon equivalent formula (1967) · Ito, Y. & Bessyo, K. (1968). Weldability formula of high strength steels related to heat-affected zone cracking. IIW Doc. IX-576-68

Checked 9 Nov 2026. Mascalco N., Koltz R., Sigler S., “Consumables Corner: Choosing the correct carbon equivalency formula”, The Fabricator / Practical Welding Today, 25 Mar 2019 (IIW, AWS D1.1 and Pcm formulas; Pcm for C below about 0.11 %).

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