Concrete Lintel Calculator
Estimate concrete for a lintel beam spanning a door, window, or other masonry opening.
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Short answer
A standard 36-inch-wide door or window opening with 8 inches of bearing on each side needs a lintel about 52 inches long. At an 8×8 inch cross-section, that’s roughly 2.4 cubic feet of concrete, or about 5 bags of 80 lb premix. Wider spans need a taller or wider lintel and usually steel reinforcement.
Typical lintel size by opening width
| Opening width | Lintel size (W×H) | Bearing each side |
|---|---|---|
| Up to 3 ft | 8 × 8 in | 8 in |
| 3–5 ft | 8 × 8 to 8 × 16 in | 8 in |
| 5–7 ft | 8 × 16 in, engineer-reviewed | 12 in |
| Over 7 ft | Engineer-specified with steel reinforcement | 12–16 in |
How to size and pour a lintel
- Measure the rough opening width for the door or window the lintel will span.
- Add the required bearing length on each side — typically 8 inches for openings under 5 feet.
- Match the lintel width to the wall thickness it sits in, and choose a height based on the span (taller for wider spans).
- Enter your dimensions above to get the concrete volume and bag count.
- Build a form supported from below, place reinforcing bar sized for the span, then pour and vibrate the concrete.
- Leave the form and shoring in place for at least 7 days, and longer for wider spans, before removing support.
Worked example
- Opening + bearing
- 36 in opening + (2 × 8 in bearing) = 52 in total length
- Volume
- 52 × 8 × 8 in = 3,328 in³ = 1.93 ft³, plus 10% waste = 2.12 ft³
- Bags (80 lb, 0.60 ft³ each)
- ceil(2.12 / 0.60) = 4 bags
Common mistakes
- Using too little bearing length, which concentrates load on a small area of masonry and can crack the wall.
- Skipping steel reinforcement on spans over about 4 feet, risking cracking or sagging under load.
- Removing the form and shoring before the concrete has cured enough to support the wall above.
- Sizing the lintel width to the opening instead of the wall thickness it needs to bear on.
Assumptions
- Standard premix concrete at roughly 150 lb per cubic foot.
- Bag yields follow manufacturer averages: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 50 lb = 0.375 ft³, 40 lb = 0.30 ft³.
- Total lintel length is the opening width plus bearing length on both ends.
- Does not include steel reinforcement, forms, or shoring cost. Spans over 4–5 feet should be engineer-reviewed.
Frequently asked questions
How much bearing does a concrete lintel need?
8 inches on each side is standard for openings up to about 5 feet. Wider spans or heavier loads above the opening may need 12 inches or more of bearing, and should be checked against local code or an engineer’s specification.
Does a concrete lintel need rebar?
Almost always, yes. Even short lintels typically include steel reinforcement near the bottom to resist bending, and spans over about 4 feet should be engineer-specified.
What size lintel do I need for a standard door or window?
An 8×8 inch lintel handles most openings up to roughly 3 to 5 feet with standard 8-inch bearing. Wider openings need a taller lintel, more bearing, or both.