Concrete Block Calculator
Find how many concrete blocks a wall needs.
Default 16 in
Default 8 in
Default 5%
Results update as you type.
How it works
Estimating concrete or cinder blocks for a wall is a common masonry task, and this calculator tells you how many blocks you need from the wall's dimensions. You enter the wall length and height, optionally adjust the block size and waste allowance, and it returns the block count and the wall area. The method is straightforward: it computes the wall's area, divides by the face area covered by a single block, and adds a waste allowance for cuts, breakage, and mistakes before rounding up to whole blocks. A standard concrete masonry unit has a nominal face of 16 by 8 inches, which includes the mortar joint, covering about 0.89 square feet, so a typical wall needs a little over one block per square foot. A waste allowance of around five percent is prudent, and you may want more for walls with many openings or corners that require cutting. This estimate covers the blocks themselves; you will separately need mortar, roughly one bag per 30 to 40 blocks, plus rebar and grout for reinforced walls. Use it for garden walls, foundations, retaining structures, and building projects to order the right quantity and avoid extra trips. Enter your wall dimensions to compute the number of concrete blocks.
Blocks = wall area / block face area × (1 + waste)
The calculator finds the wall area by multiplying length by height, then divides by the face area of one block, the block length times height converted to square feet. Multiplying by one plus the waste fraction and rounding up gives the total blocks needed, including extras for cuts and breakage. Standard blocks have a nominal 16-by-8-inch face.
Source:Masonry estimation
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter wall length and wall height.
- 2
Adjust the options
Adjust block length (in), block height (in) and waste allowance if they apply — sensible defaults are already set.
- 3
Read your result
Blocks needed updates instantly as you type — no button to press.
Frequently asked questions
How many concrete blocks do I need for a wall?
Divide the wall's area by the face area of one block, then add a waste allowance. A standard block covers about 0.89 square feet, so a wall needs roughly 1.125 blocks per square foot before waste. Enter your wall length and height and the calculator gives the exact count including extras for cuts and breakage.
What is the standard concrete block size?
A standard concrete masonry unit has a nominal face of 16 inches long by 8 inches high, which accounts for a standard mortar joint. Its actual dimensions are slightly smaller. This calculator defaults to that size, but you can enter different block dimensions if you are using a non-standard unit for your project.
How much waste should I allow?
A waste allowance of about five percent is typical for a straightforward wall, covering breakage and cutting. For walls with many corners, openings, or curves that require more cuts, allow ten percent or more. It is better to have a few spare blocks than to stop work and make another trip to the supplier.
Does this include mortar?
No, this calculator estimates only the number of blocks. You will also need mortar, roughly one 80-pound bag for every 30 to 40 blocks depending on joint size, plus sand. Reinforced walls also require rebar and grout in the cores. Estimate those materials separately once you know your block count.
How many blocks are in a square foot?
With a standard 16-by-8-inch block face covering about 0.89 square feet, there are roughly 1.125 blocks per square foot of wall. So a 100-square-foot wall needs about 113 blocks before adding a waste allowance. The exact figure depends on block size and mortar joint thickness, which the calculator accounts for.