Enter the wall’s length and height, subtract any doors and windows, and choose the block size to see how many concrete masonry units (CMU, often called cinder or breeze blocks) to buy.
Block sizes are nominal: a “16 × 8” block is really 15⅝ × 7⅝ inches, and the 3/8-inch mortar joint makes up the difference. The calculator uses the nominal size, so mortar is already accounted for.
Formula
Blocks = (Wall area − Openings) ÷ Block face area × (1 + Waste)
A 16 × 8 in block covers 128 in² = 0.889 ft², so you need 1.125 blocks per square foot. A 440 × 215 mm block with 10 mm joints covers about 0.101 m², or 9.9 blocks per m².
Worked example
A 40 ft × 8 ft wall is 320 ft². At 1.125 blocks per ft² that is 360 blocks, or 378 with 5% extra for cuts and breakage.
Frequently asked questions
How many concrete blocks are in a square foot?
1.125 standard 8 × 16 in blocks per square foot, or 112.5 per 100 ft².
How many blocks do I need per square metre?
About 10 standard 440 × 215 mm blocks per m², or 12.5 Australian 390 × 190 mm blocks.
Last updated · Calculations checked by automated tests· Editorial policy