How many bricks or blocks do I need per square metre?

These two numbers are worth committing to memory because they come out of fixed UK dimensions. A standard brick is 215 long, 102.5 wide and 65 deep in millimetres, and it is laid with a 10mm joint. That makes the working module 225 by 75, and a square metre divided by 225 by 75 comes out at 59.3 — which is where the familiar sixty comes from. The bond drawing shows the difference between the half-brick skin that takes sixty and the one-brick solid wall that takes a hundred and twenty.

Step by step

1. Measure the face area of the wall.Length times height in metres, for each wall or section. Do this for the visible face — the thickness of the wall is handled by the multiplier, not by the area.
2. Deduct openings honestly, but not entirely.Subtract windows and doors, but do not subtract every small opening, because cutting around an opening generates waste that partly cancels the saving.
3. Multiply by 60 for a half-brick wall.A single skin of brick, one stretcher thick — the outer leaf of a cavity wall, or a single-skin garden wall. This is the case most people are calculating.
4. Multiply by 120 for a one-brick solid wall.English or Flemish bond, one brick thick. It is two skins' worth of brick, so exactly double.
5. Use about 10 per square metre for standard blocks.A 440 x 215mm block laid with a 10mm joint gives a 450 x 225 module, which is 9.88 blocks per square metre. Blocks come in different thicknesses for the same face size, so the count per square metre does not change with thickness — the price does.
6. Add wastage.Five per cent on straightforward work. Ten on anything with a lot of cutting, curves, piers, arches or a decorative bond. More on reclaimed brick, where a proportion of every load is unusable.
7. Order in whole packs and check the batch.Bricks are sold in packs of a few hundred. Colour varies between production batches, so order the whole job in one delivery and one batch where you possibly can. A short order finished from a different batch shows as a patch on the wall for ever.
8. Add the mortar and the extras.Mortar, wall ties if it is a cavity, damp proof course, cavity trays, lintels, coping or capping, and a movement joint filler if the run is long enough to need one. The bricks are rarely the only thing missing from the order.

Tips

• Sixty per square metre is for standard UK bricks. Metric imperial, waterstruck, Danish and many handmade bricks have different dimensions and different counts — check the actual size before ordering.
• A pack of bricks is heavy and is delivered on a pallet. Check the delivery lorry can reach where you want it and that the ground will take a pallet truck.
• Buy the wastage. A short order at the end of a job is the most expensive brick you will ever buy, and it may not match.

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