Wood beam calculator
Enter beam depth and width, set spans and loads (point, UDL, trapezoidal), and get reactions, diagrams, deflection and serviceability checks against L/360 and L/240.
About this case
How to use this wood beam calculator
Start with the pre-loaded simply supported beam and enter your actual span. Replace the uniform load with the line load your floor or roof applies: multiply the area load in psf (or kN/m²) by the joist/rafter spacing to get plf (or kN/m). For ridge beams, enter the rafter reactions as point loads at the correct spacing.
The material preset uses timber with E = 11 GPa, density 500 kg/m³, and fy = 28 MPa; switch to a custom modulus for glulam (typically 12–14 GPa), LVL (13–14 GPa), or a specific species. Rectangular sections are entered by depth and width; the calculator derives area and I automatically.
Reading the results for a wood design check
For a quick check, compare the reported maximum bending stress against the allowable bending stress F_b from your grade stamp or the NDS supplement. For serviceability, the L/360 badge keeps floors stiff enough for tile/gypsum, and L/240 is the common roof limit. Deflection is often the governing limit for wood, not bending stress.
If the beam fails serviceability, increase the depth: deflection scales with 1/d³ (since I = bd³/12), so a 2× depth increase cuts deflection by 8× with only 2× the material. The print report includes the section properties for your calc package.
Common wood beam mistakes this tool helps you catch
Using nominal lumber dimensions instead of actual (a 2×12 is 1.5″ × 11.25″) overestimates capacity significantly. Forgetting to model the ridge as overhanging when it projects past the wall underestimates the end moment. And modeling a multi-support ridge as a series of simply supported spans misses the negative moment over the interior posts — use the continuous calculator instead.