Skip to content
ENExplore Calculators

Lintel Size Calculator

Work out lintel size instantly with clear inputs, formula shown and shareable results.

About Lintel Size Calculator

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.

Formulas

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

Worked example

With the default values below, Lintel Size Calculator returns Lintel depth required of 150. Change any input above and every figure here is recalculated in your browser.

Inputs used

Clear opening widthminimum 0.1 m
1.2 m
Load from wall aboveminimum 0.1 kN/m
12 kN/m
Bearing at each endminimum 50 mm
150 mm
Lintel widthminimum 75 mm
230 mm

Results

Lintel depth required
150 mm
Effective span
1.350 m
Design moment
4.101 kN·m
Reaction at each bearing
12.15 kN

Step by step

  1. 1Values used
  2. 2Design moment
  3. 3Depth required
  4. 4Lintel depth required= 150 mm
  5. 5Effective span= 1.350 m
  6. 6Design moment= 4.101 kN·m
  7. 7Reaction at each bearing= 12.15 kN

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Lintel design and reinforcement must be verified by a qualified structural engineer against the governing code.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Lintel design and reinforcement must be verified by a qualified structural engineer against the governing code.

Frequently Asked Questions

How is the Lintel Size figure worked out?

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.

Is the full wall above carried by the lintel?

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.

What values do I need to enter?

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.

Related Calculators

Lintel Size Calculator – Calculate Lintel depth required