Work out beam deflection instantly with clear inputs, formula shown and shareable results.
A simply supported beam with a central point load deflects PL^3/(48EI) at mid-span. The cube on span is what makes long beams so floppy: doubling the span multiplies deflection eightfold at the same load. 5 kN on a 3 m span with EI = 2 MN m2 deflects 1.4 mm, a span-to-deflection ratio well inside the usual L/360 serviceability limit.
Central point load
delta = P L^3 / (48 E I)
Serviceability check
typical limit is span / 360
Because the second moment of area goes with depth cubed. Turning a joist on edge is far more effective than making it wider.
The coefficient changes to 5wL^4/(384EI). This calculator covers the central point load case only.