By Zencalcy Editorial TeamLast reviewed About us
Carbon equivalent condenses a steel's alloy content into one number that predicts how it behaves when welded. Below 0.40 is readily weldable; above 0.50 needs preheat and controlled cooling. The IIW formula weights each element by its effect on hardenability.
Weldability from the steel's alloy content.
CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
Percentages by weight. This is the IIW (CE) formula for carbon and low-alloy steels. The Pcm formula is used for low-carbon steels, and CE becomes unreliable above about 0.6% carbon.
| Symbol | Meaning |
|---|---|
| C | Carbon, percent. |
| Mn | Manganese, percent. |
| CE | Carbon equivalent. |
CE = 0.18 + 0.20 + 0.05 + 0.007 = 0.437, which is weldable with modest preheat for thick sections.
Continue with the Beam Deflection Calculator, Beam Load Calculator, Bending Stress Calculator, or the Wood Beam Span Calculator — or browse more structural & workshop and all construction calculators.
Above 0.40, preheat 100–200°F for thin sections and more for thick ones. Above 0.50, use a qualified procedure.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
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Content updated: September 2026