Sixty per square metre
A standard brick with a 10 mm mortar joint occupies 225 × 75 mm on the face, which works out at almost exactly 60 bricks per square metre of single-skin wall. It is one of the more reliable rules of thumb in construction and it holds across most standard brick sizes.
Concrete blocks at 440 × 215 mm work out at just under 10 per square metre on the same basis. The calculator uses 10, which builds in a small margin.
The joint is part of the figure. A wall built with a 15 mm joint uses noticeably fewer bricks than one built at 10 mm, which is worth knowing if you are matching existing work — old buildings often have much thicker joints than modern practice.
| Unit | Per m² of single skin | Note |
|---|---|---|
| Standard brick, 10 mm joint | 60 | The universal figure |
| Standard brick, 15 mm joint | 55 | Common on older buildings |
| Concrete block 440 × 215 | 10 | Just under, in practice |
| Engineering brick | 60 | Same size, denser and heavier |
Single skin or cavity
The calculator works on a single skin. Almost every external wall built in the last century is a cavity wall — two skins with a gap between them — which means double the units and a set of wall ties.
The two skins are often different: facing brick outside, concrete block inside. If that is what you are building, run the calculator twice with the appropriate unit selected each time rather than doubling one figure.
Wall ties are not included. They are typically specified at 2.5 per square metre in a regular staggered pattern, with extra ties around openings and at movement joints.
Mortar, and buying more than you think
Mortar consumption is roughly 0.022 m³ per square metre for brickwork and about half that for blockwork, since blocks have far less joint area per unit of wall.
A 1:5 cement to sand mix by volume is standard for general work, needing roughly 300 kg of cement per cubic metre of mortar. Softer mixes with lime are appropriate for older or softer bricks — using a hard modern mortar on soft historic brick causes the brick face to spall rather than the joint, which is the opposite of what mortar is supposed to do.
Order sand generously. It is cheap, it is a nuisance to run short of mid-course, and the leftover has uses. Cement is the opposite — it absorbs moisture and goes off, so buy what you will use.
Common questions
How many bricks per square metre?
Sixty, for a standard brick with a 10 mm mortar joint on a single-skin wall.
How many bricks in a cavity wall?
Double the single-skin figure, since a cavity wall is two separate skins. Run the calculator twice if the skins use different units.
How much mortar for brickwork?
Roughly 0.022 m³ per square metre of single-skin brickwork, or about half that for blockwork.