Concrete Block Calculator
Count the standard 8×8×16 concrete (cinder) blocks and mortar bags for a block wall.
Calculator
| Wall area | 80.0 ft² |
|---|---|
| 80-lb bags of mortar mix (about) | 4 bags |
How it is calculated
Wall area = 20 × 4 = 80.0 sq ft. A nominal 8×8×16 block covers 8/9 sq ft with its mortar joint, so you need 1.125 blocks per sq ft: 90.0 blocks, plus 5% waste = 95.
About this calculator
A standard concrete block (also called a CMU or cinder block) is nominally 8 × 8 × 16 inches. With its mortar joint it covers 8/9 of a square foot, so a wall needs 1.125 blocks per square foot of face.
Walls taller than a few courses normally need steel reinforcement and grouted cores, and may need engineering. This calculator counts blocks only; add caps, rebar, grout and mortar-related materials separately.
Worked examples
| Project | 8×8×16 blocks (+5% waste) | Rough cost |
|---|---|---|
| a 10 ft long, 2 ft high concrete block wall | 24 blocks | $38.40 – $84.00 |
| a 20 ft long, 4 ft high concrete block wall | 95 blocks | $152 – $332 |
| a 30 ft long, 6 ft high concrete block wall | 213 blocks | $341 – $746 |
| a 40 ft long, 8 ft high concrete block wall | 378 blocks | $605 – $1,323 |
Buying notes
- The blocks per course are the wall length in inches divided by 16: a 20-foot wall needs 15 blocks per course.
- Half blocks at corners and ends add to the count; the 5% allowance covers some of it.
- Check local rules on footings, height limits and reinforcement.
Quick answers by size
Click a size for the exact quantity and cost.
How to measure and use this calculator
- Measure the wall's length and height.
- Enter them to get the block count based on standard 8×8×16 blocks.
- Add cap blocks, rebar and grout separately for tall or structural walls.
- Check local rules on footings and wall height.
Common mistakes
- Using nominal block sizes with the wrong joint assumption.
- Forgetting half blocks at corners and ends.
- Building tall walls without reinforcement.
Tips
- A standard nominal block is 8 in tall and 16 in long, which gives 1.125 blocks per square foot.
- Walls taller than a few feet usually need rebar and grout in the cores; those are not counted here.
- Check local code for footing and height limits before building a freestanding wall.
Frequently asked questions
How many cinder blocks per square foot?
A standard 8×8×16 block covers about 0.89 sq ft of wall, so plan on 1.125 blocks per square foot.
How many cinder blocks per square foot?
A standard 8×8×16 block covers about 0.89 sq ft of wall, so plan on 1.125 blocks per square foot.
How many blocks are in one course of a 20 foot wall?
A 20-foot wall is 240 inches long, divided by 16 inches per block gives 15 blocks per course.