How to Calculate Concrete Blocks Needed

Standard concrete blocks (CMUs) are 16 inches long and 8 inches tall including the mortar joint, so a wall needs roughly 1.125 blocks per square foot of wall area — but the real-world number always comes from wall area minus openings, not a flat multiplier.

Measure total wall length × height for the gross area, then subtract the area of any doors, windows, or other openings before converting to a block count. Skipping this step is the single most common source of over-ordering.

The Concrete Block Calculator handles the openings subtraction and estimates mortar bags alongside the block count.