Concrete Block Calculator
Enter the length and height of your wall, subtract doors and windows and choose the size of the block to see how many concrete blocks to buy. Block size and waste are editable.
How to use this concrete block calculator
- Measure the length and height of the wall in feet.
- Subtract the area of doors and windows. Enter the total in square feet, or leave it at 0.
- Enter the face size of one block, including the mortar joint. The default is 16 by 8 inches, the face of a standard 8x8x16 block.
- Keep the waste allowance or change it, then add the optional mortar and price figures.
- Press Calculate. Use Copy result or Export CSV to take the counts to your supplier.
How to calculate how many concrete blocks you need
The calculator divides the wall area by the area of one block face.
- Net wall area = length x height – openings
- Blocks per square foot = 144 / (block face length x block face height), in inches
- Blocks = net area x blocks per sq ft x (1 + waste % / 100), rounded up
- Mortar bags (optional) = blocks / blocks per bag, rounded up
Worked example
A garden wall is 30 ft long and 6 ft high, so the area is 180 sq ft with no openings. A block face of 16 by 8 inches is 128 sq in, so there are 144 / 128 = 1.125 blocks per square foot. The exact count is 180 x 1.125 = 202.5, which rounds up to 203. With 5% waste you need 212.6, so 213 blocks.
If the wall has a 3 ft by 4 ft window, subtract 12 sq ft from the area first. That saves about 14 blocks before waste. Remember to ask your supplier about special blocks for corners and the top course.
Assumptions & limits
- The wall is a plain rectangle laid in a running bond with standard blocks. Corners, lintels, bond beams and half blocks are not counted separately.
- The block face size is the nominal size, which includes the mortar joint. Real blocks are slightly smaller than the nominal size.
- Mortar coverage varies by product and mason. The mortar bag figure is optional and entirely your own input.
- Footings, rebar and grout fill are not included. Use the Concrete Footing and Rebar calculators for those.
- Check local code and ask an engineer for walls that hold back soil or carry a load.
Frequently asked questions
How do I calculate how many concrete blocks I need?
Multiply the wall length by its height to get the area, subtract openings, and divide by the face area of one block. A 16 by 8 inch block gives 1.125 blocks per square foot.
How many 8x8x16 blocks are in a square foot?
A block that measures 16 by 8 inches on its face takes 128 square inches, so 144 / 128 = 1.125 blocks cover one square foot.
How much waste should I allow?
Five percent is a common allowance for breakage and cuts. Walls with many corners or openings may need more.
Does the count include half blocks and corners?
No. It is a simple area estimate. Ask your supplier for corner, half and bond beam blocks.
How much mortar do I need?
It depends on the mortar and the mason. Enter blocks per bag from your product label to get an estimate.
Can I use other block sizes?
Yes. Enter the face length and height in inches for the block you choose.
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Last updated: November 2026