This free steel I-beam load capacity calculator estimates the maximum uniformly distributed load a beam can safely carry based on its span, section size, and steel grade. Use it for quick checks on wide-flange (W) and standard (S) sections before detailed design.
For a simply supported beam with a uniformly distributed load, the maximum bending moment is M = wL² / 8, and bending stress is σ = M / S, where S is the section modulus. Setting the stress to the allowable bending stress Fb gives the safe distributed load:
w = 8 · Fb · S / L²
Here w is load per unit length, L is the clear span, and Fb ≈ 0.66 Fy for compact sections in allowable-stress design (about 24 ksi / 165 MPa for ASTM A36, Fy = 36 ksi). Long spans are often governed by deflection (typically L/360) rather than stress, so always check both.
Representative section modulus (Sx) and allowable moment for common wide-flange beams in A36 (Fb ≈ 24 ksi):
| Section | Sx (in³) | Allowable moment (kip·ft) |
|---|---|---|
| W8×18 | 15.2 | 30.4 |
| W10×22 | 23.2 | 46.4 |
| W12×26 | 33.4 | 66.8 |
| W14×30 | 42.0 | 84.0 |
| W16×40 | 64.7 | 129.4 |
Values are for preliminary estimation only. Verify against current AISC tables and a qualified engineer before construction.
Find the beam's section modulus (S), multiply by the allowable bending stress (about 24 ksi for A36 steel) to get the allowable moment, then convert to a safe uniformly distributed load with w = 8FbS/L2, where L is the span. Long spans should also be checked for deflection.
They compute the same thing from different angles: a strength calculator focuses on the beam's bending capacity (allowable moment), while a load capacity calculator converts that capacity into the distributed or point load the beam can carry over a given span.
Yes. Higher-yield steels such as A992 (Fy = 50 ksi) allow a higher bending stress than A36 (Fy = 36 ksi), so the same section can carry more load. Enter the correct grade so the allowable stress matches your steel.
Bending moment grows with the square of the span (L2), so doubling the span cuts the safe distributed load to about one quarter. This is why long beams need deeper sections or intermediate supports.
Calculate the maximum load capacity and deflection of steel I-beams based on span, beam size, and loading conditions.
| Designation | Depth (in) | Weight (lb/ft) | Area (in²) | Ix (in⁴) | Sx (in³) |
|---|