Beam Deflection Calculator
Calculate the expected deflection of a simply-supported wood or steel beam under a center point load.
About the Beam Deflection Calculator
This calculator gives a simplified estimate of how much a simply-supported rectangular beam will sag (deflect) under a single load applied at its center, using standard beam theory. It's a quick check for framing decisions, not a substitute for a structural engineer's analysis on load-bearing applications.
Formula: I = (Width × Depth³) ÷ 12; Deflection (δ) = (P × L³) ÷ (48 × E × I), where P is the load, L is the span in inches, E is the material's modulus of elasticity and I is the moment of inertia.
Most building codes limit deflection to L/360 for floors under live load — compare your result against the allowable deflection shown above. Increasing beam depth reduces deflection far more than increasing width, since depth is cubed in the formula.