Lintel Quantity Calculator
Enter opening width, quantity and wall thickness to get lintel length, concrete volume, formwork and a suggested depth.
Inputs
Result
Formula
| Length per lintel | L = opening width + 2 × bearing |
| Suggested depth | h = opening ÷ 8 (round up to 50 mm, min 120 mm) |
| Concrete | V = L × wall thickness × h × quantity |
| Formwork | A = (2 × L × h + L × wall thickness) × quantity |
10 openings 1.2 m wide, 240 mm wall, 250 mm bearing, depth left at 0: depth auto 0.15 m, 1.70 m per lintel, 17 m total, 0.612 m³ concrete, 9.18 m² formwork.
FAQ
Why must a lintel bear into the wall, and how far?
The lintel must transfer load into the masonry either side, not merely span the gap. 250 mm per end is standard; 300-370 mm for openings over 1.5 m; more in seismic zones or where the wall end is close to the opening. Too short a bearing crushes the wall end — a very common defect.
Precast or cast-in-situ lintels?
Precast is fast, formwork-free and consistent — ideal for standard openings in volume, chosen straight from the album. Cast-in-situ gives better integrity and handles non-standard sizes, heavy loads or monolithic casting with ring beams, at the cost of formwork and curing time.
Must the depth always be opening / 8?
1/8 is a starting rule of thumb; the code requirement is a real bending and shear check against the actual wall load above. Large openings, tall walls above, or concentrated loads (padstones, canopies) must be checked rather than proportioned. Seismic zones add minimum reinforcement ratios and stirrup densifying.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.