Beam Deflection Check

Tool

Simply supported beam under a uniformly distributed load: δ = 5 w L⁴ / (384 E I). Enter unfactored (SLS) loading. Common limits: L/360 (general), L/500 (below brittle finishes), L/250 (total including permanent).

Span L(m)SLS UDL w(kN/m)Second moment I(cm⁴)Young's modulus E(N/mm²)Deflection limit

Output

Enter inputs and press Calculate to see results.

Tool version 1.0 · Last reviewed March 2026

Method and assumptions

· Simply supported beam carrying a uniformly distributed load: δ = 5 w L⁴ / (384 E I).
· Loading entered is unfactored (serviceability limit state).
· Elastic behaviour, uncracked prismatic section, no allowance for creep, shrinkage, pre-camber or construction sequence.
· Allowable deflection is taken as L divided by the selected limit (L/250, L/360 or L/500).

Worked example

Span L = 6.0 m, SLS UDL w = 10 kN/m, I = 21 500 cm⁴, E = 210 000 N/mm², limit L/360.
δ = 5 × 10 × 6000⁴ / (384 × 210 000 × 21 500 × 10⁴) ≈ 3.7 mm.
Allowable = 6000 / 360 = 16.7 mm — the check passes.

Disclaimer

Indicative result only. The calculation depends on the assumptions and information entered and does not constitute structural design or professional advice. Do not use the result for construction, procurement, Building Regulations submissions or safety-critical decisions. All results must be independently verified by a suitably qualified structural engineer before being used for design, construction or regulatory purposes. Bebbington Engineering Studio Ltd accepts no responsibility for reliance placed on unverified results.