What does a concrete block calculator measure?
A concrete block calculator estimates how many concrete masonry units, or CMU blocks, you need for a wall. It uses the wall length, wall height, openings, block face size, and extra allowance.
The calculator works from the block face. For a standard 8 in. by 16 in. nominal face, one block covers 128 square inches of wall face, including the mortar joint. That is about 0.89 sq ft.
The output is a block count. It does not include mortar, grout, rebar, footings, or engineering requirements.
How is concrete block calculated?
The wall area is:
Wall area = wall length x wall heightThen the calculator subtracts openings:
Net wall area = wall area - openingsNext, it converts the block face from square inches to square feet:
Block coverage = block face square inches / 144The base block count is:
Blocks = net wall area / block coverageThe calculator rounds up to whole blocks. If you enter extra for cuts or breakage, it applies that before the final rounding.
How to use this concrete block calculator
- Enter the wall length and height in feet.
- Enter any openings to subtract in square feet.
- Choose the nominal block face size.
- Add any extra allowance your supplier or mason recommends.
- Read the block count, base count, and net wall area.
Use nominal block face size for this estimate. Home Depot explains that nominal CMU dimensions include the mortar joint, while actual blocks are slightly smaller.
Example: standard block wall
Say you are planning a wall 20 ft long and 6 ft high.
20 x 6 = 120 sq ftA standard 8 in. by 16 in. nominal face covers:
8 x 16 = 128 sq in
128 / 144 = 0.89 sq ftThe base block count is:
120 / 0.89 = 135 blocksIf you add 5% extra, the order count is:
135 x 1.05 = 141.75The calculator rounds up to 142 blocks.
Common CMU face sizes
CMHA notes that concrete masonry units commonly use nominal face dimensions. The thickness of the block can change, but the face is often based on an 8 in. high module.
| Nominal face | Face area | Coverage |
|---|---|---|
| 8 in. x 16 in. | 128 sq in | 0.89 sq ft |
| 8 in. x 8 in. | 64 sq in | 0.44 sq ft |
| 8 in. x 12 in. | 96 sq in | 0.67 sq ft |
Actual products vary by local block producer. Check the block schedule or product page before ordering.
What to check before building
Concrete block walls can be structural, retaining, decorative, or nonbearing. The block count is only one part of the project.
Check local code, footing size, reinforcement, drainage, height limits, and whether the cells need grout. For engineered or retaining walls, use a qualified professional.
For nearby projects, the Drywall Calculator can estimate panel count, and the Interior Painting Cost Calculator can estimate paint after interior work is done. You can also browse all Home Improvement calculators.
Limitations
This calculator estimates block count from wall face area. It does not know bond pattern, pilasters, corners, bond beams, lintels, partial blocks, waste from damaged units, or local code.
It also does not estimate mortar or grout. Those depend on wall design, joint size, block shape, and whether cells are filled.