Concrete Lintel Calculator
This concrete lintel calculator sizes cast-in-place lintels over doors, windows and openings: total length (clear span plus both bearings), width and depth, times the number of lintels. Remember: the concrete volume is easy — the reinforcement design is what makes a lintel work.
How to Use This Calculator
- Enter your dimensions — feet for lengths, inches for thickness.
- Adjust the options — waste percentage, bag size and your local concrete price.
- Read your results — volume, bags, weight and cost update live as you type.
The Formula
Lintel volume = (span + 2 × bearing) × width × depth × count Worked example: A lintel over a 48 in opening with 6 in bearings each end, 8 × 8 in section: 60 × 8 × 8 in = 2.2 ft³ — about 4 × 80 lb bags each.
Lintel length is span plus bearing: standard practice is at least 6 inches (150 mm) of bearing each end, more for heavier loads — so a 4 ft opening needs a 5 ft lintel.
Cast-in-place lintels are usually matched to the wall width (8 inches for standard block) with depth of 8 inches for door/window spans; longer spans need engineered depth and reinforcement — typically 2 bars top and bottom with stirrups on wider openings.
Small volumes make lintels a bagged-concrete job, but use a structural mix: M20/3,000 psi minimum, fully rodded into the form around the rebar cage.
Frequently Asked Questions
Common questions about the concrete lintel calculator.
How long should a lintel be?
Clear opening plus at least 150 mm (6 in) bearing each end. A 900 mm window needs a 1,200 mm lintel.
How much concrete per lintel?
Length × width × depth. A 5 ft × 8 in × 8 in lintel is about 2.2 ft³ — roughly 4 × 80 lb bags.
What reinforcement does a lintel need?
Residential door/window lintels typically carry 2 × #4 bars bottom (tension) with #3 stirrups; anything over ~6 ft span or carrying point loads should be engineered.
Precast or cast-in-place?
Precast is faster and quality-controlled; cast-in-place suits odd sizes and continuous bond-beam construction. Volume math here covers the cast-in-place case.
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