Concrete Block Calculator (UK)
Last updated: 12 August 2026
Work out how many concrete blocks you need for a wall, plus the mortar and wall ties to go with them. Based on the standard UK 440 × 215mm block.
How the calculation works
The maths here is unusually clean. A standard UK block is 440 × 215mm. Add a 10mm mortar joint and the coordinating size becomes 450 × 225mm = 0.10125 m², so ten blocks fill one square metre almost exactly. We then add 5% for cuts.
Mortar is estimated at 0.00065 m³ per block plus 25% waste — that comes from a 440 × 100 × 10mm bed joint plus a 215 × 100 × 10mm perpend. Wall ties for cavity walls are calculated at 2.5 per m², which corresponds to the standard 900mm horizontal × 450mm vertical spacing.
Block sizes and coverage
| Block size | Per m² | Typical use |
|---|---|---|
| 440 × 215 × 100mm | 10 | Standard inner leaf, partitions |
| 440 × 215 × 140mm | 10 | Thicker walls, better acoustics |
| 440 × 215 × 215mm | 10 | Solid walls, foundations |
| 440 × 100 × 215mm (on flat) | ~21 | Coursing blocks |
Block thickness does not change the number per square metre of wall face — only the mortar volume and the weight you are lifting.
Wall tie spacing
Standard cavity walls take ties at 900mm horizontal and 450mm vertical centres — 2.5 ties per square metre. Around openings and at unbonded edges, ties drop to 300mm vertical centres within 225mm of the opening. Wide cavities and exposed sites need 4.4 per square metre. Always check the current Approved Document A and the tie manufacturer specification.
Frequently asked questions
How many concrete blocks are in a square metre?
Exactly 10. A standard 440 x 215mm block with a 10mm mortar joint has a coordinating size of 450 x 225mm, which is 0.10125 square metres — so ten blocks fill one square metre of wall.
How many blocks do I need for a 10 metre wall?
A 10m long by 2.4m high single-skin wall is 24 square metres, which needs 240 blocks. Add 5% for cuts and order 252.
What size is a standard UK concrete block?
440 x 215mm face, most commonly 100mm thick for inner leaves and partitions. 140mm and 215mm thicknesses are used where more strength, acoustic performance or a solid wall is needed.
How many wall ties do I need per square metre?
2.5 per square metre for standard cavity walls, from 900mm horizontal by 450mm vertical spacing. Increase to 4.4 per square metre for wide cavities or exposed sites, and add extra ties within 225mm of every opening at 300mm vertical centres.
How much mortar do I need per block?
About 0.00065 cubic metres per 100mm block with 10mm joints — a 440 x 100 x 10mm bed joint plus a 215 x 100 x 10mm perpend. Per 100 blocks that is roughly 0.08 cubic metres of mortar including waste, which is about 0.1 tonnes of sand and one bag of cement.
Related calculators
Brick Calculator
How many bricks for your wall — UK sizes, mortar bags and wastage.
Mortar Calculator
Sand, cement and ready-mix bags for bricks or blocks.
Concrete Calculator
Slab and footing volumes in m³, with bag counts or ballast & cement.
Estimates are for guidance only. Material dimensions, densities and coverage vary by supplier — always confirm quantities before ordering, and consult a qualified professional for structural work.