Beam calculator
Three-check beam analysis: bending stress, deflection, and horizontal shear per NDS reference values.
How Beam Sizing Works
A beam must pass three independent checks to be structurally adequate. Failing any one means the beam is undersized for that condition, even if it passes the other two.
The Three Checks
1. Bending (Fiberstress) — The beam must resist the bending moment without exceeding the allowable bending stress (Fb) for the species and grade. This check compares the required section modulus against what the beam provides.
2. Deflection — The beam must not deflect more than L/360 for floors or L/240 for roofs. Excessive deflection causes bouncy floors, cracked finishes, and visible sag even if the beam is structurally safe.
3. Horizontal Shear — Wood beams can fail along the grain near the supports. The actual shear stress (fv = 3V/2bd) must not exceed the allowable shear stress (Fv).
What load should I enter?
Total load = dead load + live load, expressed in pounds per linear foot of beam. For a typical residential floor beam: dead load ~10-15 psf, live load 40 psf, multiplied by the tributary width. A beam carrying 8 feet of floor at 50 psf total would have 400 lbs/ft total load.