This block wall calculator estimates how many concrete blocks (CMUs) you need from the wall’s length and height, plus the mortar to lay them. Enter your wall dimensions above to get the block count, mortar bags, and a waste allowance.
How to use this calculator
- Enter the wall length and height in feet.
- Subtract any large openings (doors, gates) if needed.
- Read the block count and mortar bags in the results.
How is the block count calculated?
A standard 16″ × 8″ block covers 0.89 ft² of wall face, so each square foot needs about 1.125 blocks:
Wall area (ft²) = Length × Height Blocks = Wall area × 1.125 × (1 + waste %)
- 1.125 — blocks per ft² for a standard 16×8 CMU
- Waste % — add ~5% for cuts and breakage
Example calculation
For a 20 ft long, 8 ft tall wall:
- Wall area = 20 × 8 = 160 ft²
- Blocks = 160 × 1.125 = 180
- Add 5% waste → order 189 blocks
At ~3 bags of mortar per 100 blocks, plan for about 6 bags.
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Frequently Asked Questions
How many blocks do I need for a wall?
There are about 1.125 standard 16 x 8 inch blocks per square foot of wall. Multiply wall area by 1.125, then add 5 percent for breakage.
What size is a standard concrete block?
A standard CMU is nominally 16 inches long by 8 inches high by 8 inches wide, including the mortar joint, giving a face area of about 0.89 square feet.
How much mortar do I need for a block wall?
Plan on roughly three 80-lb bags of mortar per 100 blocks, adjusting for joint thickness and your mix.