Calculate how many concrete blocks (CMU) and bags of mortar you need to build a wall. Supports 8×8×16, 8×8×8, 4×8×16, and 12×8×16 blocks with door and window openings.
Quick reference for standard 8×8×16 block walls with no openings.
| Wall (L × H) | Area (sq ft) | Blocks | Mortar bags |
|---|---|---|---|
| 10 × 4 ft | 40 | 48 | 5 |
| 20 × 4 ft | 80 | 95 | 9 |
| 20 × 8 ft | 160 | 189 | 17 |
| 40 × 8 ft | 320 | 378 | 33 |
| 50 × 8 ft | 400 | 473 | 41 |
Building a 20×8 foot block wall with no openings? You need 189 standard 8×8×16 CMU blocks (including 5% waste) and 17 bags of 80-lb mortar mix. At $1.50–$3.00 per block, budget $284–$567 for blocks plus $136–$204 for mortar.
For standard 8×8×16 CMU blocks, you need 1.125 blocks per square foot of wall. This accounts for the block plus the 3/8-inch mortar joint. A 100-square-foot wall needs 113 blocks before adding waste.
Plan for approximately 8.5 bags of 80-lb mortar mix per 100 blocks. A 200-block wall needs about 17 bags. Type S mortar is recommended for load-bearing and below-grade walls, while Type N works for non-load-bearing above-grade walls.
CMU (Concrete Masonry Unit) is the industry term for concrete blocks. 'Cinder block' is an older term from when coal cinders were used as aggregate. Modern blocks use concrete aggregate and are properly called CMU. The terms are often used interchangeably in practice.
An 8-foot wall requires 12 courses of standard 8-inch-high CMU blocks (96 inches / 8 inches per course = 12 courses). Each course includes the block height (7-5/8 inches actual) plus a 3/8-inch mortar joint, totaling 8 inches nominal.
Most block walls over 4 feet tall or any load-bearing wall require vertical rebar every 48 inches and horizontal rebar every 16–24 inches per code. The rebar-filled cores are then grouted with concrete. Check your local building code for specific requirements.
Standard 8×8×16 CMU blocks cost $1.50–$3.00 each. For a 160-square-foot wall (about 189 blocks with 5% waste), budget $285–$570 for blocks and $136–$204 for mortar. Professional installation adds $10–$17 per square foot of wall face.
Need brick instead of block? Try our brick calculator for standard modular brick walls and veneer.
Typical Results
💡 If block count seems too high, check that you subtracted door and window openings from the wall area.
Common Mistakes