Concrete Block Calculator
Enter your wall's length and height to find how many concrete blocks (CMUs) you need, plus the mortar bags. A standard 8x8x16 block with a 3/8-inch mortar joint covers 1.125 blocks per square foot of wall.
How to calculate concrete block
Find the wall's face area in square feet (length × height), then multiply by 1.125, the number of standard 8×8×16-inch concrete blocks per square foot once you allow for a 3/8-inch mortar joint. Round up, add about 10% for cuts and breakage, and plan one 80-pound bag of mortar for every 33 blocks.
Blocks = Wall area ft² × 1.125 (standard 8×8×16 CMU + 3/8" mortar)
Worked example
A block wall 20 ft long and 8 ft high (160 ft²).
- Area = 20 × 8 = 160 ft²
- Blocks = 160 × 1.125 = 180 blocks
- Mortar = 180 ÷ 33 = 6 bags
Result: 180 blocks (order ~198 for 10% waste), plus 6 bags of mortar
Frequently asked questions
How many concrete blocks do I need?
Multiply the wall's length by its height for the area in square feet, then multiply by 1.125 blocks per square foot. A 160 ft² wall needs about 180 standard blocks. Add 10% for cuts and breakage.
How many concrete blocks are in a square foot?
A standard 8×8×16-inch concrete block (CMU) with a 3/8-inch mortar joint covers a 16×8-inch face, which works out to 1.125 blocks per square foot of wall.
Is a cinder block the same as a concrete block?
For estimating, yes. Cinder block is the common name for a concrete masonry unit (CMU). Both use the same nominal 8×8×16-inch size, so the count of 1.125 blocks per square foot applies to either.
How much mortar do I need for a block wall?
Plan on one 80-pound bag of mortar mix for roughly every 33 standard blocks, so about 3 bags per 100 blocks. A 180-block wall needs around 6 bags.
How many blocks do I need for a 10x10 wall?
A 10 ft × 10 ft wall is 100 square feet, so it needs about 113 standard 8×8×16 blocks (100 × 1.125), or roughly 125 with a 10% waste allowance.
How much extra should I order for waste?
Add about 10% to your block count. Corners, openings, and the occasional cracked block mean you'll always use more than the bare wall area suggests.