Work out how many blocks you need. This free concrete block calculator divides wall area by block face, subtracts doors and windows, adds waste, and estimates mortar bags — in feet or metres.
Wall
ft
ft
in
in
ft²
%
Enter the wall size and pick your block. Subtract the area of any doors or windows, and add a waste allowance (5–10% typical) for cuts and breakage.
Blocks needed
—
Enter wall size
Net wall area
—
Blocks (before waste)
—
Blocks per area unit
—
Mortar (≈, 60 lb bags)
—
Blocks = net wall area ÷ block face area, rounded up after waste. A standard 16 × 8 in block covers about 0.89 ft², so roughly 1.125 blocks per square foot. Mortar is a rough guide (about one 60 lb bag per 30–35 blocks).
Use this free concrete block calculator to work out how many blocks you need for a wall. Enter the wall size and block type, subtract any openings, and add waste for an accurate count.
What this concrete block calculator does
A concrete block calculator divides your wall area by the face area of one block to find how many blocks (CMUs) you need, after subtracting doors and windows and adding a waste allowance. It also estimates mortar bags.
How the block count is calculated
net area = (wall length × height) − openings
blocks = net area ÷ block face area, × (1 + waste %)
A standard 16 × 8 in block covers about 0.89 ft², so roughly 1.125 blocks per square foot. A 20 × 8 ft wall (160 ft²) needs about 180 blocks, or ~198 with 10% waste.
Common block sizes
Block face
Coverage
Blocks per ft²
16 × 8 in (standard CMU)
0.89 ft²
1.125
12 × 8 in
0.67 ft²
1.5
8 × 8 in
0.44 ft²
2.25
440 × 215 mm (UK)
0.095 m²
~10.6 / m²
Don’t forget openings and waste
Subtract the area of doors and windows so you don’t over-order, but always add 5–10% waste for cuts, breakage and corners. The calculator rounds up to whole blocks.
How to use the concrete block calculator
Enter the wall length and height.
Pick the block size (or enter a custom face).
Subtract openings, add waste, and read the block count.
Concrete Block FAQ
How many concrete blocks do I need?
Divide your net wall area by the block's face area, then add waste. A standard 16 × 8 in block covers about 0.89 ft², so a 160 ft² wall needs roughly 180 blocks (about 198 with 10% waste).
How many blocks are in a square foot?
About 1.125 standard 16 × 8 in blocks per square foot. Smaller blocks cover less, so you need more per square foot.
Should I subtract doors and windows?
Yes. Enter the total opening area and the calculator removes it from the wall before counting blocks.
How much waste should I add?
Usually 5–10% to cover cuts, breakage and corners. The calculator rounds up to whole blocks.
How much mortar will I need?
As a rough guide, about one 60 lb bag of mortar per 30–35 blocks. The calculator shows an estimate; confirm with your mix and supplier.
Is the concrete block calculator free?
Yes, this concrete block calculator is completely free, needs no sign-up, and gives instant results in your browser.
