1
Measure the wall
Enter the total wall length and height.
Free Masonry Calculator
Concrete Block Calculator – Blocks, Wall Area & Cost
Estimate how many concrete blocks or CMU blocks you need for a wall. Calculate wall area, subtract door and window openings, add waste and estimate material cost.
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Wall Details
Enter the wall dimensions, openings and block size. Results update automatically.
Wall coverage depends on block face length and height. Block thickness does not change the face area used for this estimate.
Use nominal block dimensions when estimating modular concrete masonry walls. Actual block dimensions and mortar joints may differ by product and supplier.
How many concrete blocks do I need?
Calculate the wall area by multiplying wall length by wall height. Subtract the area of doors, windows and other openings. Then divide the remaining wall area by the face area of one block and add a waste allowance.
How to Use the Concrete Block Calculator
2
Subtract openings
Enter the combined area of doors, windows and other openings.
3
Choose block size
Use a common CMU size or enter a custom block face size.
4
Add waste
Add extra blocks for cuts, breakage and project adjustments.
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Concrete Block Formula
First calculate the net wall area.
Wall Area − Opening Area = Net Wall Area
Then divide the net wall area by the face area of one block.
Net Wall Area ÷ Block Face Area = Blocks Required
Concrete Block Calculation Example
For a 20 ft × 8 ft wall using nominal 8 × 8 × 16 inch blocks:
20 × 8 = 160 square feet
Block face area = 16 × 8 ÷ 144 ≈ 0.889 ft²
160 ÷ 0.889 ≈ 180 blocks
With 5% waste = 189 blocks
Common Concrete Block Sizes
Concrete masonry units are available in many thicknesses and sizes. For wall coverage, the block face length and height are the most important dimensions.
8 × 8 × 16 inCommon nominal CMU
6 × 8 × 16 in6 in thick CMU
4 × 8 × 16 in4 in thick CMU
Custom blockEnter face dimensions
Why Add Extra Blocks?
Extra blocks can help cover cuts, breakage, damaged units, layout changes and measurement differences. The appropriate allowance depends on the wall design and job conditions, so the waste percentage is adjustable.
Concrete Block Calculator FAQ
How many concrete blocks do I need per square foot?+
The number depends on the face dimensions of the block. A nominal 16 by 8 inch block covers about 0.889 square feet, so the theoretical requirement is about 1.125 blocks per square foot before waste.
Should I subtract windows and doors?+
Yes. Subtract the total area of large openings such as doors and windows from the gross wall area before calculating the block quantity.
Does block thickness change the number of blocks?+
For a single wall face, block thickness normally does not change the wall coverage. The face length and height determine how many blocks cover the wall area.
Should I add extra blocks for waste?+
Adding extra blocks can help account for cuts, breakage and site adjustments. The calculator includes an adjustable waste allowance.
Can I use custom concrete block dimensions?+
Yes. Enter the face length and face height of the block you plan to use.
Does this calculator include mortar?+
This tool estimates the number of concrete blocks. It does not calculate mortar quantity because joint thickness, block type and installation method can vary.
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Planning Disclaimer
This calculator provides planning estimates. Actual block requirements can vary because of block dimensions, mortar joints, bond pattern, cuts, breakage, wall design and site conditions. Confirm final quantities and construction requirements with your supplier or project professional before ordering.