Standard concrete masonry units are 8 x 8 x 16 in nominal. The real block is 3/8 in smaller each way, which leaves room for the mortar joint.
Concrete block calculator
Enter the wall length and height and any openings. Results are for standard 8 x 8 x 16 in block.
Enter your numbers to see the result.
Blocks per square foot
With its joint, each block covers 8 x 16 = 128 sq in. A square foot is 144 sq in, so a wall takes 144 / 128 = 1.125 blocks per square foot.
A wall 40 ft long and 6 ft high is 240 sq ft: 270 blocks, or 284 with 5% extra for breakage and cuts.
Mortar and sand
The calculator uses one masonry supplier’s published quantities for 8 in block: about 25 bags of masonry cement and 5 tons of sand per 1,000 blocks. Mortar use changes with joint size and the mason, so treat it as a starting order.
What the count leaves out
- Corner, bond beam and half blocks: count them from your layout.
- Grout and rebar for filled cores, which structural walls often need.
- Footings: use the concrete calculator with the footing option.
Retaining walls and load-bearing walls usually need a design and a permit. Check before you build.
Sources
Sources last checked 1 November 2026.
Frequently asked questions
How many blocks are in a square foot?
1.125 standard 8 x 8 x 16 in blocks, because each one covers 128 sq in with its joint.
How many bags of mortar per 100 blocks?
About 2.5 bags of masonry cement per 100 blocks (25 per 1,000) by one supplier’s published figures, plus about half a ton of sand.
What are the real dimensions of an 8x8x16 block?
7-5/8 x 7-5/8 x 15-5/8 in. The 3/8 in difference is the mortar joint.