Concrete Block Calculator
Short answer: a 20 ft long, 8 ft high wall needs about 177 blocks (16 × 8 in blocks, 3/8 in joints, 5% waste). Enter your wall below.
Calculate your blocks
How the calculation works
Wall area = length × height. Each block covers (block length + joint) × (block height + joint). Blocks = wall area ÷ block face area, rounded up per course and with your waste allowance.
Worked example: a 20 × 8 ft wall = 160 sq ft. A 16 × 8 in block with 3/8 in joints covers 0.95 sq ft, so 160 ÷ 0.95 = 168 blocks net, 177 with 5% waste (12 courses, about 15 blocks per course).
Common wall sizes (16 × 8 in blocks, 3/8 in joints)
| Wall | Blocks (5% waste) | Courses |
|---|---|---|
| 10 ft × 4 ft | 45 | 6 |
| 20 ft × 4 ft | 89 | 6 |
| 20 ft × 8 ft | 177 | 12 |
| 30 ft × 8 ft | 265 | 12 |
Blocks are rounded up from the wall area, then waste is applied. Courses are shown for laying out.
Frequently asked questions
How many concrete blocks do I need for a 20 foot wall?
For a 20 ft long, 8 ft high wall with standard 16 × 8 in blocks and 3/8 in joints: 177 blocks with 5% waste, in 12 courses of 15.
How do you calculate concrete blocks for a wall?
Divide the wall area by the face area of one block including its mortar joint, round up per course, then add 5% for cuts and breakage.
What size is a standard concrete block?
The standard face size is 16 inches long by 8 inches high. Common thicknesses are 8, 10 and 12 inches — thickness does not change the block count for a wall face.