Concrete block calculator: how many concrete blocks do I need?
113 blocks
100 square feet of wall takes 113 concrete blocks of the standard 8 by 16 inch nominal face, because one block covers 0.89 square feet including its mortar joint.
100 square feet of surface · for 12.5 × 8 ft
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
113 blocks
100 square feet of surface
A worked example
A 23 by 6 ft retaining wall in 12 × 16 in block, 5 % waste needs 109 blocks. 138 square feet at 1.33 square feet per block is 103.5, and the allowance takes it to 109.
What else it is called
A concrete block is also sold as a cement block, a cinder block or a CMU, short for concrete masonry unit. True cinder blocks made with coal ash are rarely produced today, so in practice all four names point at the same 8 by 16 inch nominal face, and the count on this page does not change with the name on the pallet.
Common sizes
| Area | 8 × 16 in | 4 × 16 in | 12 × 16 in | 8 × 8 in |
|---|---|---|---|---|
| 8 × 8 ft — 64 sq ft | 72 | 144 | 48 | 144 |
| 10 × 10 ft — 100 sq ft | 113 | 225 | 75 | 225 |
| 10 × 12 ft — 120 sq ft | 135 | 270 | 90 | 270 |
| 12 × 12 ft — 144 sq ft | 162 | 324 | 108 | 324 |
| 12 × 16 ft — 192 sq ft | 216 | 432 | 144 | 432 |
| 16 × 20 ft — 320 sq ft | 360 | 720 | 240 | 720 |
| 20 × 20 ft — 400 sq ft | 450 | 900 | 300 | 900 |
Pieces, rounded up, with no waste allowance added.
Where the numbers come from
- Block coverage is the nominal face you select, multiplied out: an 8 by 16 inch nominal block covers 0.89 square feet. Nominal sizes already include the mortar joint, which is why the arithmetic works without adding one.
This counts stretcher blocks for a straight wall. Corners, bond beams and half blocks are extra, and how many depends on your layout.
Last checked September 26, 2026. How this site is made.