Work out blocks, mortar and ties
Standard 440 × 215 mm blocks with 10 mm joints: 10 per m². Choose a single leaf or a cavity wall with a brick outer leaf.
Openings to take off
Mortar = joint volume from the block size + the extra %. Building sand ≈ 1.6 t per m³ of mortar; cement at 1.4 t/m³ loose. Ties = 2.5 per m² plus extra up each side of every opening at 300 mm centres.
Quantities are estimates for ordering. Wall tie type, spacing and mortar strength must follow the design and the manufacturer's data.
Blocks per m², mortar and wall ties
The figures the calculator uses.
| Block | Blocks / m² | Joints m³/m² | +60% m³/m² | Blocks / m³ |
|---|---|---|---|---|
| 100 mm | 10 | 0.0066 | 0.0105 | 952 |
| 140 mm | 10 | 0.0092 | 0.0147 | 680 |
| 215 mm | 10 | 0.0141 | 0.0226 | 443 |
One block plus its joint covers 450 × 225 mm, so 1 m² takes 9.9 — counted as 10. “Blocks / m³” is how many blocks one cubic metre of mortar lays with the allowance.
| Item | Per m² |
|---|---|
| Facing bricks (outer leaf) | 60 |
| 100 mm blocks (inner leaf) | 10 |
| Wall ties | 2.5 |
| Mortar, both leaves | 0.039 m³ |
Wall ties at 900 mm horizontal × 450 mm vertical centres (2.5 per m²), with extra ties at 300 mm vertical centres within 225 mm of the sides of openings.
How many blocks in a square metre?
A standard UK concrete block has a 440 × 215 mm face. With 10 mm joints each one covers 450 × 225 mm, so a square metre takes 9.9 blocks — 10 per m² is the figure everyone uses. The count is the same whatever the thickness (100, 140 or 215 mm); only the weight and the mortar change.
Example: a 6 m × 2.4 m wall with one 1.2 × 1.2 m window is 14.4 − 1.44 = 12.96 m² → 130 blocks, 137 with 5% waste.
Cavity walls
A typical cavity wall has a facing brick outer leaf (60 bricks per m²) and a block inner leaf (10 per m²), tied together across the cavity. Approved Document A and LABC guidance put wall ties at a maximum of 900 mm horizontally and 450 mm vertically — which works out at 2.5 ties per m² — with extra ties at no more than 300 mm vertical centres within 225 mm of the sides of openings, movement joints and verges. Tie type and length depend on the cavity width and the design, so check the specification.
Mortar for blockwork
The joints of a 100 mm block wall hold about 0.0066 m³ of mortar per m²; the calculator adds 60% for droppings and thicker beds. That works out at roughly 1 m³ of mortar for 950 blocks, close to the rule of thumb of about 800 blocks per m³. Thicker blocks need proportionally more.
Questions bricklayers ask
How many blocks are in a square metre?
Ten. A 440 × 215 mm block with 10 mm joints covers 450 × 225 mm, which is 9.9 blocks per m². The number is the same for 100, 140 and 215 mm thick blocks.
How many wall ties per square metre?
For a standard cavity wall with leaves at least 90 mm thick, ties go at a maximum of 900 mm horizontal and 450 mm vertical centres, which is 2.5 ties per m². Add ties at 300 mm vertical centres within 225 mm of each side of openings.
How many blocks does a cubic metre of mortar lay?
Roughly 800 to 950 standard 100 mm blocks, depending on bed thickness and waste. Thicker blocks need proportionally more mortar per block.
How many bricks and blocks for a cavity wall per m²?
About 60 facing bricks for the outer leaf and 10 blocks for the inner leaf per square metre of wall, plus 2.5 wall ties and the mortar for both leaves.
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Take-off on the PDF drawings, a real bill of quantities and quotes clients sign — bricks, blocks, labour and margin in one place.
See Graftum estimatingQuantities are estimates for ordering. Wall tie type, spacing and mortar strength must follow the design and the manufacturer's data.