Universal Beam Calculator — UB Size Selection & Load Check

M = wL²/8 is the bending moment formula for a simply supported beam with a uniformly distributed load (UDL). 'w' is the load per metre (kN/m), 'L' is the clear span in metres. It applies to most domestic floor beams, lintels, and similar simply supported conditions. For point loads or cantilevers, different formulae apply.

Deflection is a serviceability check, so it is verified under the characteristic combination of variable (imposed/live) loads only — permanent (dead) loads are excluded. The UK National Annex to BS EN 1993-1-1 gives span/360 for beams carrying plaster or other brittle finishes and span/200 for other beams. For beams supporting masonry, common UK practice tightens this to span/500 (or stricter, up to span/600) to keep movement small enough to avoid cracking the brittle masonry — this matches the span/500 brittle-partition limit in the UK National Annex to BS EN 1990. Pick the value that matches what your beam supports.

S275 is the standard grade for most UK structural steelwork — it has a yield strength of 275 N/mm². S355 (yield 355 N/mm²) is stronger and used where weight or depth must be minimised. S355 costs slightly more per tonne but you often use less steel, so it can work out cheaper overall. Most steel stockholders carry both grades.

A typical allowance for connection plates, bolts, cleats, and stiffeners is 10-15% of the main steel weight. For simple beam-to-column connections, 10% is usually adequate. For moment connections, portal frame haunches, or complex fabrications, allow 15% or more. Your steelwork fabricator can give a precise figure from their shop drawings.

Yes, but you must work out the correct UDL first. As a rule of thumb, where the wall above is tall enough for arching to develop, only a triangle of masonry actually loads the beam — the rest is carried by the masonry either side. BS 5977-1 (the recognised UK lintel-loading method) uses a 45° load triangle with its base equal to 1.1 × the clear span (the masonry within this triangle is carried by the beam), plus a 60° interaction zone outside it where point loads are dispersed and halved. Add this triangular masonry load to any floor or roof loads bearing on the beam. Confirm the exact load triangle and interaction zone from BS 5977-1 or your structural engineer. For padstone and bearing details, see our RSJ Installation Calculator.