Enter the yield strength of the material and the (elastic) section modulus into the calculator to determine the elastic yield moment (often called “moment capacity” in simplified section-strength checks).

Moment Capacity Calculator

Pick a steel section and grade to get the bending capacity (My, Mp, and LRFD φMp).

Beam Capacity
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Moment Capacity (Elastic Yield Moment) Formula

The following formula is used to calculate the elastic yield moment of a cross section:

M = Fy * S

Unit note: If Fy is in psi (lb/in²) and S is in in³, then M comes out in lb-in. To convert to lb-ft, divide by 12: M (lb-ft) = Fy · S / 12.

Variables:

  • M is the elastic yield moment (lb-in, or lb-ft after dividing by 12)
  • Fy is the yield strength of the material (psi)
  • S is the elastic section modulus (in^3)

To calculate the elastic yield moment, multiply the yield strength of the material by the elastic section modulus, then convert to your desired moment units if needed.

What is Moment Capacity?

In this calculator, “moment capacity” refers to the elastic yield moment: the bending moment at which the extreme fiber stress first reaches the material’s yield strength. It is a measure of the section’s bending strength based on material yield stress and cross-sectional shape (via section modulus). In real design, the usable capacity may be lower due to additional limit states such as lateral-torsional buckling, local buckling, or connection/bracing conditions.

How to Calculate Moment Capacity?

The following steps outline how to calculate the Moment Capacity:

  1. First, determine the yield strength of the material (Fy) in psi.
  2. Next, determine the elastic section modulus (S) in cubic inches (in³).
  3. Next, use the formula from above: M = Fy · S (this gives M in lb-in when Fy is in psi and S is in in³).
  4. Finally, if you want M in pound-feet, convert lb-in to lb-ft by dividing by 12.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Yield strength of the material (Fy) = 36,000 psi

Section modulus (S) = 10 in^3

Elastic yield moment: M = 36,000 × 10 = 360,000 lb-in = 30,000 lb-ft