About the Concrete Block Calculator
Concrete blocks are laid in courses with a mortar joint, so the number needed for a wall depends on the size of the block plus the joint. This calculator takes the wall area, the block type and a waste allowance and returns the number of blocks to order. It supports the standard American 16 by 8 inch block and the metric 440 by 215 millimetre block used in the UK and elsewhere. Type the wall area, the block size and the waste allowance and the concrete blocks appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Concrete Block Calculator
- 1Enter the wall area, the block size and the waste allowance.
- 2Pick the units or options from the menus if the concrete blocks tool offers them.
- 3Read the concrete blocks in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the concrete blocks
Builders use it to order blocks for walls, garages, sheds, retaining walls and garden barbecues. DIY builders use it to compare the cost of blocks with bricks and to plan deliveries by the pallet.
Subtract the area of door and window openings from the wall area before you enter it. A larger opening saves a lot of blocks. Also add blocks for any piers, corners and lintels, which this tool does not count.
How the concrete blocks is worked out
Blocks per area = 1 ÷ (block length including joint × block height including joint). A 16 × 8 inch block covers 128 square inches, so 1.125 blocks cover a square foot. A 440 × 215 mm block with a 10 mm joint takes up 450 × 225 mm. A wall of 10 square metres built from 440 × 215 mm blocks needs 9.88 blocks per square metre, so 99 blocks, and with 5 percent waste, 104. A 100 square metre wall of 16 × 8 inch blocks needs 12.1 blocks per square metre, 1,272 with 5 percent waste.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- US and metric blocks
- Per-area counts
- Waste allowance
Mistakes to avoid with concrete blocks
The sizes are the nominal sizes, including the mortar joint, so the tool does not add a joint again for the US block. Blocks are often sold by the pallet, so round up to a full pallet. Check your local supplier's block dimensions, which vary.
On phone and computer
On a phone, type into the boxes one after another and read the concrete blocks underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the concrete blocks move. The concrete block calculator works the same on both. Combine it with Brick Calculator for a mixed wall, Concrete Calculator for the footing, Area Calculator for the wall size, and Tile Calculator for any finishing.
Features
- Subtract openings first
- Round up to pallets
- Check local dimensions
- Clear messages when the concrete blocks inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate concrete blocks?
Blocks per area = 1 ÷ (block length including joint × block height including joint). A 16 × 8 inch block covers 128 square inches, so 1.125 blocks cover a square foot. A 440 × 215 mm block with a 10 mm joint takes up 450 × 225 mm. A wall of 10 square metres built from 440 × 215 mm blocks needs 9.88 blocks per square metre, so 99 blocks, and with 5 percent waste, 104. A 100 square metre wall of 16 × 8 inch blocks needs 12.1 blocks per square metre, 1,272 with 5 percent waste.
What is the formula for concrete blocks?
Blocks per area = 1 ÷ (block length including joint × block height including joint). A 16 × 8 inch block covers 128 square inches, so 1.125 blocks cover a square foot. A 440 × 215 mm block with a 10 mm joint takes up 450 × 225 mm. The concrete block calculator applies it exactly and rounds only the displayed answer to six significant figures.
How many blocks are in a square foot?
1.125 for a standard 16 × 8 inch block.
How much mortar do I need?
It depends on the joint thickness; ask your supplier. One bag usually lays a limited number of blocks.
Should I add extra for waste?
Yes, 5 percent for simple walls and up to 10 percent for walls with many cuts.
Is this concrete block calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.