Beam Deflection Calculator
Calculate maximum deflection of a simply supported or cantilever beam under point or uniform distributed load using standard structural engineering formulas.
Results
What is it?
Beam deflection is the vertical displacement of a beam under load. Excessive deflection causes structural and aesthetic problems — codes typically limit deflection to span/360 for floors and span/240 for roofs. This calculator covers the four most common loading cases using the standard EI (flexural rigidity) formula.
How to use
Select the beam support and load type. Enter the total applied load in kN, the beam span in metres, the elastic modulus of the material (200 GPa for steel, 30 GPa for concrete, 12 GPa for timber), and the second moment of area from section tables.
Example scenario
A 203×203 UC52 steel beam (I = 5259 cm⁴) spans 6 m with a 20 kN point load at midspan. E = 200 GPa. Deflection = (20,000 × 6000³) / (48 × 200,000 × 5259 × 10⁴) = 5.7 mm. Span/deflection = 6000/5.7 ≈ L/1053 — well within L/360 limit.
Pro tip
The Span/Deflection ratio is the key serviceability check. Most building codes require L/360 minimum for floors (ratio ≥ 360) and L/180 for wind drift. If your ratio is below the required value, increase the beam section or reduce the span.