Concrete Block Calculator
Net wall area subtracts openings. Divide by block face, apply waste from 0 to 40 percent, and round up. A common CMU face is 16 by 8 in, or about 1.333 by 0.667 ft. Estimate only, not a permit, code check, or engineered design.
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How to estimate concrete blocks
- Enter wall length and height in one unit.
- Enter block length and block height in that same unit (defaults match a 16 by 8 in face in feet).
- Enter openings area to subtract and waste from 0 to 40 percent.
- Read net wall area, blocks before waste, and blocks to buy. Mortar and bond beams need extras.
CMU face count
Wall face minus openings with waste
| Net area | max(0, length × height - openings) |
|---|---|
| Block face | blockLength × blockHeight |
| Buy | ceil(raw × (1 + waste/100)) |
| Common CMU | 16×8 in face ≈ 1.333×0.667 ft |
| Waste bound | 0 to 40 percent |
| Omitted | Mortar joints, bond beams, and half-blocks |
What this CMU count covers
Face-bedded block count on a rectangular wall. Retaining walls with optional depth sit on retaining wall. Clay brick courses sit on brick. Grout and footing volume can start from concrete.
How blocks to buy are computed
area = max(0, length × height - openings). face = blockLength × blockHeight. raw = area / face. buy = ceil(raw × (1 + waste/100)). Units must match. Mortar joint thickness is not subtracted unless you shrink the block face yourself.
Nominal vs actual CMU size
A nominal 16 by 8 by 8 block often measures about 15.625 by 7.625 by 7.625 in. Many takeoffs still use nominal face. Bond beams, lintels, and half blocks at openings need extras. Rebar in cells sits on rebar only as a separate sketch.
Use cases
A 40 by 8 ft wall with 1.333 by 0.667 ft block faces and 5% waste, minus door area. Comparing waste levels. Not a structural masonry design.
Limits
No joint thickness field and no grout fill volume. Estimate only, not a permit, code check, or engineered design. See the disclaimer.