Work out lintel size instantly with clear inputs, formula shown and shareable results.
A lintel is designed as a simply supported beam whose effective span is the clear opening plus one bearing length. The factored uniform load gives a moment of wL²/8, and for a singly reinforced M20 section the limiting moment of resistance is 0.138 fck b d², which inverted gives the effective depth needed. Cover and bar radius add about 40 mm to reach overall depth.
Design moment
M = 1.5 w L² / 8, L = clear span + bearing
Depth required
d = sqrt(M / (0.138 fck b)), overall depth = d + 40 mm
Preliminary estimate only. Lintel design and reinforcement must be verified by a qualified structural engineer against the governing code.
M = 1.5 w L² / 8, L = clear span + bearing. A lintel is designed as a simply supported beam whose effective span is the clear opening plus one bearing length.
Not always. Masonry can arch over a short opening so only a triangular load reaches the lintel, but that relies on adequate abutment either side and is not assumed for openings near a corner.
This calculator takes 4 inputs: Clear opening width, Load from wall above, Bearing at each end, Lintel width. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.