Concrete Block Calculator

Work out how many concrete blocks (CMUs) you need for a wall. Enter the wall size and block dimensions to get the block count, including the mortar joint and a waste allowance.

Block calculator

Wall length (ft) Wall height (ft)

Unit length (in) Unit height (in) Mortar joint (in) Waste %

Unit size includes the mortar joint. The blocks count is exact; the mortar figure is a rough estimate from standard ratios — confirm against your mortar's coverage.

How it's calculated

We work out the face area of one block including its mortar joint — (length + joint) × (height + joint) — convert your wall area into that many blocks, add a waste allowance, and round up. A standard 16 × 8 inch block covers about 1.125 blocks per square foot.

Frequently asked questions

How many blocks do I need?

Divide the wall area by the face area of one block including its mortar joint, then add waste. A standard 16 × 8 inch block works out to about 1.125 blocks per square foot.

How many concrete blocks per square foot?

About 1.125 standard 16 × 8 inch blocks per square foot of wall.

How much mortar for concrete block?

Roughly 3 bags of mortar per 100 blocks. The calculator shows a rough estimate.

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Last updated June 2026.