The job
Modelled, not recorded. Every figure here is the answer the Brick Calculator gives for these inputs, written down in both unit systems and re-run whenever the site is built. No job was carried out, so there is no measured overrun on this page.
The wall is the flank of a single-storey rear extension: 6.5 m (21.33 ft) along the boundary side and 2.6 m (8.53 ft) from the footing to the wall plate, with no windows or doors in it, which is common on a side that faces a neighbour. It is a cavity wall, and this count is its outer leaf only, in a facing brick chosen to match the house.
The brick is the UK standard size, entered as the calculator asks for it, by its actual dimensions: 215 mm long, 65 mm high and 102.5 mm deep, laid with 10 mm joints. The calculator opens on the US modular brick instead, so these four inputs are the difference between a British count and an American one.
The allowance is set to 5 per cent, below the calculator's default. A plain wall with no openings and stretcher bond throughout needs few cut bricks, and new facing bricks bought by the pack arrive with few rejects; the reclaimed-brick variant below is the case for more.
The inputs, exactly as entered
| Input | Value | Why |
|---|---|---|
| Wall Length | 6.5 m (21.33 ft) | Along the face of the outer leaf from the corner of the house to the extension's rear corner. |
| Wall Height | 2.6 m (8.53 ft) | From the top of the footing to the underside of the wall plate; the courses below ground are part of the count. |
| Waste Factor (%) | 5 | Lower than the calculator's default, for a plain wall in new bricks with no openings to cut around. |
| Brick actual length | 215 mm (8.46 in) | The actual length of the UK standard brick, not the coordinating size that includes a joint. |
| Brick actual height | 65 mm (2.56 in) | The actual height of the brick; with the joint it sets the course height. |
| Mortar joint width | 10 mm (0.39 in) | The usual UK bed and perpend joint. |
| Brick depth (wall thickness) | 102.5 mm (4.04 in) | The bed depth of the brick, which is the thickness of a half-brick outer leaf and sets the mortar volume. |
The working, step by step
1. Wall area
16.9 m² (181.9 sq ft)
Length times height gives the face of the wall, 16.9 m². The calculator has no openings input, which is why a wall without windows was chosen; on a wall with them, the openings would be taken off before entering the area.
2. Coverage rate (from your dimensions)
59.26 bricks/m² (5.51 bricks/sq ft)
Each brick with its joint occupies a rectangle on the face of the wall, and one square metre divided by that rectangle gives 59.26 bricks/m². That is the figure UK bricklayers carry in their heads, here worked out from the brick and the joint rather than remembered, which is the calculator's first source's point: bricks vary, so the rate should follow the brick.
3. Base brick count (no waste)
1,002 bricks
The face area times that rate is 1,002 bricks, the count if every brick went into the wall whole. The allowance is then added and the result rounded up, which gives the headline.
4. Mortar mix needed
24 x 25 kg bags
The mortar is worked out from the space the joints occupy through the depth of the wall: the gap between the brick and its coordinating size, over the whole face. At the dry mix yield in the calculator's second source that comes to 24 bags of the size a UK merchant stocks, a figure that assumes premixed mortar rather than sand and cement mixed on site.
Estimated brick needed
1,052 bricks
Order 1,052 bricks for the outer leaf, from one batch, because facing bricks vary in colour between firings and a wall laid from two batches can show the change as a band. Bricks are sold by the pack, so the order is rounded to packs at the merchant. The inner leaf of the cavity wall is usually blockwork, counted separately, and the cavity insulation, wall ties and the cavity tray at the junction with the house are all separate items too.
What to buy
| Quantity | Figure | What it is for |
|---|---|---|
| Estimated brick needed | 1,052 bricks | Facing bricks for the outer leaf, from one batch, with the allowance included. |
| Mortar mix needed | 24 x 25 kg bags | Premixed mortar for the outer leaf only, in the merchant's standard bag; mixing on site instead uses the mortar mix calculator. |
The allowance, and what it does here
The 5 per cent goes on the whole brick count once. On a plain stretcher-bond wall it covers the half bricks at the ends of alternate courses where the wall returns, the occasional brick that breaks on the bolster, and a few rejected for chips or colour. It is not enough for a wall with many openings and reveals, for a decorative bond with headers, or for reclaimed bricks with old mortar to clean off, which is the variant below.
The common mistake
Counting with the calculator's default brick
The calculator opens on the US modular brick, and a UK reader who types in the wall and leaves the brick alone gets a count for a smaller brick than the one being laid: about a quarter too many, as the variant below shows. The bricks per square metre is the figure to check; if it is not close to the rate a bricklayer quotes for the brick on site, the brick dimensions are wrong. Enter the actual size of the brick being bought, from the maker's data sheet, before reading any count.
Change the job, and see what moves
The same wall, in a reclaimed brick with more rejects
Waste Factor (%): 10 → 1,102 bricks
Build the same wall in reclaimed bricks, where more are rejected for damage or old mortar, at 10 per cent, and the order rises to 1,102 bricks. The wall and the coverage rate are unchanged; only the allowance moves, so the difference is exactly the extra share.
The same wall, in a US modular brick
Brick actual length: 193.7 mm (7.63 in); Brick actual height: 57.15 mm (2.25 in); Mortar joint width: 9.53 mm (0.38 in); Brick depth (wall thickness): 92.08 mm (3.63 in) → 1,310 bricks
Put the US modular brick back into the same wall, the brick the calculator opens on, and the count becomes 1,310 bricks, because the smaller brick lays at 73.81 bricks/m². The wall has not changed at all, which is the reason to enter the real brick every time.
What to run next
- Mortar Mix Calculator (ASTM C270 Types M, S, N, O)
If the mortar is mixed on site rather than bought premixed, this turns its volume into cement, lime and sand for the mix specified.
- Cavity Wall Weep Hole Spacing Calculator
The outer leaf needs weep holes above the damp-proof course and over any cavity tray, counted along the same length.
- Brick Movement Joint Spacing Calculator
A long run of clay brickwork needs movement joints at intervals, which this wall's length should be checked against.
Sources
The method and every constant behind these figures belong to the Brick Calculator, version 2.0.1, last verified 2026-09-03. It rests on:
- Bricks per square foot is derived geometrically from nominal brick face dimensions (actual brick size + mortar joint width) rather than a single fixed rate, since brick products and joint widths vary
- Mortar volume is derived from the gap between actual and nominal brick face dimensions across the wall's depth; one 80 lb bag of mortar mix yields approximately 0.66 cubic feet when mixed, a rate of 0.00825 cubic feet per pound of dry mix — which puts the 25 kg bag metric merchants stock at about 12.9 litres
Frequently asked questions
- How many bricks for a 6.5 by 2.6 m wall?
- In UK standard bricks with 10 mm joints, a half-brick leaf takes 1,002 bricks before the allowance and 1,052 bricks with 5 per cent added.
- How many bricks are in a square metre?
- For the UK standard brick and joint, 59.26 bricks/m², worked out from the brick and the joint. A different brick gives a different rate, which is why the calculator asks for the brick's size.
- How much mortar does the wall need?
- The calculator works it from the joints: 24 bags of premixed mortar at its stated yield for the outer leaf of this wall.