Understanding This Calculator
Concrete masonry units (CMU), commonly called cinder or concrete blocks, are sized to a consistent 8x8x16in nominal footprint, which makes estimating a wall straightforward once you know the exposed face area. This calculator converts your wall’s square footage directly into a block count using the standard 0.89 sq ft face coverage per block, plus a waste allowance for cuts and breakage.
Mortar bag estimates for block work follow a different ratio than brick, since each block covers far more area per mortar joint. Budgeting roughly 3 bags of mortar mix per 100 blocks laid is the standard trade rule of thumb for a single-wythe wall with typical 3/8in joints.
- 0.89 face sq ft covered by one standard 8x8x16in block
- 1.05 5% waste factor for cuts and breakage
| Wall Area (sqft) | Approx. Blocks | Approx. Mortar Bags |
|---|---|---|
| 100 | ~118 | 4 |
| 250 | ~295 | 9 |
| 500 | ~590 | 18 |
Frequently Asked Questions
Does the block count include rebar or grout fill?
No, this calculates only the number of concrete blocks and mortar for the joints. If you plan to fill cores with concrete, use our Cinder Block Fill Calculator to estimate that volume separately.
Why 0.89 sqft per block instead of the full 8x16in face?
A block’s nominal 8x16in dimension includes the mortar joint allowance, so the actual face area used for coverage math works out to about 0.89 sqft per unit once joints are factored in — this matches standard masonry estimating tables.