Block Calculator
Work out how many concrete blocks a wall needs — with mortar joints and wastage counted — for US 16×8 in blocks and UK 440×215 mm blocks.
Concrete blocks are big, so a small error in the joint size changes the count by whole blocks. This calculator uses the same exact cell method as the brick calculator — each block plus its share of mortar joint.
It covers the two standard sizes: US 16×8 in and UK 440×215 mm, with any joint size you enter.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Measure the wall length and height.
- Enter your block size — US 16 × 8 in or UK 440 × 215 mm.
- Set the mortar joint (10 mm / 3/8 in) and wastage (10%).
- Add a price per block for a cost estimate.
Worked example
| Wall (US) | 20 ft × 8 ft = 160 ft² |
|---|---|
| Block + joint | (16 + 0.375) × (8 + 0.375) in = 137.1 in² = 0.952 ft² per block |
| Raw blocks | 160 ÷ 0.952 = 168 blocks |
| With 10% wastage | ⌈168 × 1.10⌉ = 185 blocks |
| Wall (UK) | 10 m², 440 × 215 mm + 10 mm joint → about 10 blocks/m² → 110 blocks with wastage |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How many blocks per square metre?
About 10 for a UK standard block (440 × 215 mm) with a 10 mm joint. For a US standard block (16 × 8 in) with a 3/8 in joint, about 1.05 blocks per square foot. The calculator works it out exactly for your block size.
What is the difference between a block and a brick?
Size, mainly: a standard block is about four times the face area of a brick, so block walls go up faster and use less mortar per square metre. Blocks are usually used for structural walls and foundations; bricks for facing and detail.
Do I need to allow for the mortar?
Yes — the joints are counted in this calculator via the cell method, so the block count already includes the mortar space. Use the mortar calculator for the mortar volume itself.
Should I deduct openings?
Yes. Subtract windows, doors and other openings from the wall area before calculating, or the calculator will count blocks for a wall that is not there.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.