How to use the simple beam point load deflection calculator
This page works out the deflection of a simply supported beam carrying one point load. Choose a load at midspan or at any position along the span, then describe the section either by rectangular width and depth or by entering the moment of inertia directly. The result lists the moment of inertia, the deflection under the load, the span divided by that deflection, and the position at which the largest deflection occurs.
A central load uses d = PL^3 / (48EI), and an off-center load uses the deflection under the load, d = Pa^2b^2 / (3EIL), where b is the span minus a. The position of the maximum is found with x = sqrt((L^2 - b^2)/3), taking b as the shorter segment, and is reported as a distance from the support on the longer side. At midspan the two expressions agree, and there the deflection under the load is the maximum. The modulus of elasticity stays an input because no per-material default is confirmed in an authoritative source here. The sources are secondary and current as of October 2026.
Uniform loads, cantilever deflection and any verdict against an allowable deflection limit are not covered. This is a reference aid and does not replace design work; review by a qualified engineer is required.
Frequently asked questions
The equations used here give the deflection under the load and the position at which the maximum occurs. An expression for the value at that position is not confirmed in an authoritative source here, so it is left out.
It changes with the material and the grade, and no per-material default is confirmed in an authoritative source here. Use the figure from the standard or the mill report you are working to.
It does not. This page covers point loads on a simply supported span only; uniform loads and cantilever deflection belong to separate tools.