Work out the safe load capacity of a steel I-beam from a real section database. Pick the section, the steel grade and the span, and the calculator runs both the bending-strength check and the deflection check, then tells you which one governs and what load the beam can actually carry.
Allowable-stress estimate: Fb = 0.66 Fy, E = 200 GPa, compact and laterally supported section, static load, beam self-weight not deducted. Not a substitute for code-compliant design — check lateral-torsional buckling, shear and load combinations with a qualified engineer.
Two independent limits are evaluated and the smaller one wins:
Because deflection scales with L⁴ and moment only with L², the deflection check takes over as spans get longer — which is why a long beam often needs a deeper section rather than a stronger steel.
| Section | Ix (in⁴) | Sx (in³) | Weight (lb/ft) | Ix (cm⁴) | Sx (cm³) |
|---|---|---|---|---|---|
| W8×18 | 61.9 | 15.2 | 18 | 2576.5 | 249.1 |
| W10×22 | 118 | 23.2 | 22 | 4911.5 | 380.2 |
| W12×26 | 204 | 33.4 | 26 | 8491.1 | 547.3 |
| W14×30 | 291 | 42 | 30 | 12112.3 | 688.3 |
| W16×40 | 518 | 64.7 | 40 | 21560.8 | 1060.2 |
| W18×50 | 800 | 88.9 | 50 | 33298.5 | 1456.8 |
| W21×62 | 1330 | 127 | 62 | 55358.7 | 2081.2 |
| W24×76 | 2100 | 176 | 76 | 87408.5 | 2884.1 |
The calculator holds 66 W-shapes plus 16 IPE and 12 HEB sections with their published Ix and Sx values.
Take the section modulus S of the beam, multiply by the allowable bending stress (0.66 x yield) to get the allowable moment, then convert to a load using the formula for your support and loading case. For a simply supported uniform load, w = 8M/L². Then check deflection separately — on longer spans it usually governs.
Short, heavily loaded beams are normally governed by bending strength. Longer beams are governed by deflection, because deflection grows with the fourth power of span while moment grows with the square. This calculator runs both checks and reports the lower capacity.
L/360 is standard for floors supporting brittle finishes, L/240 for general floor and roof framing, and L/180 for some roof members. The stricter the limit, the lower the allowable load.
It changes the bending capacity in proportion to yield strength — A992 (345 MPa) carries about 38% more moment than A36 (250 MPa) in the same section. It does not change deflection at all, because all structural steels share the same modulus of elasticity (200 GPa).
No. It is an allowable-stress estimate for compact, laterally supported, simply supported or cantilever beams under static load. Real design must account for lateral-torsional buckling, web shear and crippling, load combinations and code factors. Always have a qualified engineer verify.
Related tools: Beam Span · Beam Deflection · Metal Weight · Beam Cost · All calculators
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) |
|---|