Concrete block calculator
Building a block wall, garden bed, or shed foundation? Enter the wall’s length and height plus your block size, and this concrete block calculator tells you exactly how many blocks to buy — including extra for cuts and breakage.
How the concrete block calculation works
Concrete blocks are sold by nominal face size: a standard block covers 16 × 8 inches of wall face (the actual block is 15⅝ × 7⅝ in — the missing ⅜ in is the mortar joint). The calculator divides your wall into courses: blocks per course come from wall length ÷ block length, and the number of courses from wall height ÷ block height, each rounded up because you can’t buy part of a block.
A waste allowance covers cut blocks at corners and ends plus breakage. Flat, straight walls need about 5%; walls with openings, corners, or steps need around 10%.
blocks = ⌈(length_ft × 12 ÷ block_length_in)⌉ × ⌈(height_ft × 12 ÷ block_height_in)⌉ × (1 + waste%)
Concrete block calculator FAQ
How many concrete blocks do I need for a 10 ft long, 8 ft high wall?
With standard 16×8 in blocks: 8 blocks per course × 12 courses = 96 blocks, plus 5% waste = 101 blocks. Enter your exact dimensions above for your wall.
What size is a standard concrete block?
The standard nominal size is 16 × 8 × 8 inches. The actual block measures 15⅝ × 7⅝ × 7⅝ inches — the ⅜-inch difference is the mortar joint, which is why you calculate with 16 × 8.
How many concrete blocks are in a square foot?
One standard block covers 128 square inches of wall face, so you need about 1.125 blocks per square foot (144 ÷ 128).
How much extra should I order for waste?
5% is enough for simple straight walls. Add 10% if the wall has corners, openings, or steps that need cut blocks.
Do I need to subtract the mortar joints?
No. Nominal block dimensions (16 × 8 in) already include a ⅜-inch mortar joint, so the calculator’s count is correct as-is.
Can I use this for a retaining wall?
The block count works the same, but retaining walls need proper drainage, footing depth, and often engineering — check your local building code before you build.