A UK standard 440 × 215mm block covers 10 per square metre with a 10mm mortar joint. A US 16 × 8 in CMU covers 12.5 per m², and a UK brick 60 per m².
Multiply the wall area by that figure, subtract openings, add wastage, and you have your order. The parts that trip people up are what counts as an opening and how much wastage to allow.
Units per square metre
| Unit | Face size | With 10mm joint | Per m² | Per 100 ft² |
|---|---|---|---|---|
| UK concrete block | 440 × 215mm | 450 × 225mm | 9.9 | 92 |
| EU block | 500 × 200mm | 510 × 210mm | 9.3 | 87 |
| US CMU | 16 × 8 in | 410 × 205mm | 11.9 | 111 |
| UK brick | 215 × 65mm | 225 × 75mm | 59.3 | 551 |
| US brick (modular) | 194 × 57mm | 203 × 68mm | 72.5 | 674 |
The conventional figures quoted in the trade are 10 blocks per m² and 60 bricks per m², which round the exact numbers up slightly and build in a small margin. Both are fine to work with.
Working from wall dimensions
Multiply length by height to get the gross area, then subtract openings.
A wall 8m long and 2.4m high is 8 × 2.4 = 19.2 m². At 10 blocks per m² that’s 192 blocks gross.
Subtract a door opening 0.9 × 2.1m (1.89m²) and a window 1.2 × 1.2m (1.44m²), total 3.33m². Net area is 15.87m², so 159 blocks.
Then add wastage.
How much wastage
| Situation | Wastage allowance |
|---|---|
| Simple rectangular wall, no openings | 3–5% |
| Wall with a few openings | 5% |
| Multiple openings, returns, piers | 7–10% |
| Curved or angled work | 10–15% |
| Delivery breakage (aircrete) | Add 2–3% |
Cuts are the main source of waste. Every opening produces cut blocks at its edges, and the offcuts are rarely the right size to use elsewhere. Aerated blocks also chip more readily in handling than dense ones.
On the example above, 159 blocks plus 7% is 170 blocks. Order to the next full pack — packs are typically 60 to 100 blocks depending on type.
Double-skin walls
A cavity wall has two leaves, so double the count. The outer leaf may be brick and the inner block, in which case calculate each separately from the same area.
For a 19.2m² cavity wall with a brick outer and block inner: 19.2 × 60 = 1,152 bricks, plus 19.2 × 10 = 192 blocks. Wall ties at 2.5 per m² gives 48 ties, though check the specified spacing for your wall height.
Mortar quantities
Blockwork uses roughly 0.02m³ of mortar per m² of wall at a 10mm joint. Brickwork uses more — around 0.03m³ per m² — because there are far more joints.
| Wall area | Blocks | Mortar | Sand | Cement (25 kg) |
|---|---|---|---|---|
| 10 m² | 100 | 0.20 m³ | 0.34 t | 3 |
| 20 m² | 200 | 0.40 m³ | 0.68 t | 6 |
| 50 m² | 500 | 1.00 m³ | 1.70 t | 15 |
| 100 m² | 1,000 | 2.00 m³ | 3.40 t | 30 |
Figures assume a 1:5 cement to sand mortar. The block calculator gives block counts and mortar for your wall dimensions and block size.
Bond patterns and cutting
Stretcher bond — each course offset by half a block — is standard for blockwork and produces the least waste, because every course starts and ends with a half block that pairs with its opposite.
Other bonds increase both the block count and the cutting. Stack bond, with joints aligned vertically, needs reinforcement in the bed joints because there is no interlock, and it is structurally weaker.
Every opening produces four cut blocks per course at its jambs. A wall with three openings might need forty cuts, and cutting is slow work — budget time as well as material.
Piers and returns
Freestanding walls over about 1.2m high need piers for stability, typically at 3m centres and at every end and corner. A pier is usually one block deep by two wide, bonded into the wall.
Each pier adds roughly 4 blocks per course. On a 2m high wall that is 9 courses, so 36 extra blocks per pier — easy to leave out of an estimate and enough to leave you short.
Returns and corners also consume blocks faster than a straight run, because the bond has to be maintained through the corner.
Worked example
A garden wall 10m long and 1.8m high, single skin, with two piers.
- Wall area:
10 × 1.8 = 18 m² - Blocks at 10 per m²: 180
- Two piers, 8 courses, 4 blocks each: 64
- Subtotal: 244
- Wastage at 7%: 17
- Order: 261 blocks, rounded to 4 packs of 70
Mortar for 18m² at 0.02m³/m² is 0.36m³, plus extra for the piers — call it 0.45m³, which is around 0.75 tonnes of building sand and 7 bags of cement.
Ordering and delivery
Order all the blocks for one wall in a single delivery where you can. Concrete blocks vary slightly in colour between production batches, and on a wall that will be left fair-faced rather than rendered, a second delivery partway up shows as a visible band.
Blocks come banded on pallets, typically 60 to 100 per pack depending on type and weight. Order in whole packs — merchants rarely split them, and part packs cost more per unit.
Think about where the pallets will land. A pack of dense blocks weighs over a tonne, and a delivery lorry with a crane needs firm ground and clear overhead access. Getting 1,000 blocks dropped at the front of a house when the wall is at the back adds a full day of barrowing.
Foundations for a block wall
A block wall needs a footing, and its size follows from the wall rather than the blocks. The general rule is a footing twice the wall thickness wide and at least 200mm deep, sitting below frost depth on undisturbed ground.
For a single-skin 100mm wall that means a 300mm wide footing at 200mm deep, typically 450mm below ground for a garden wall. For a 215mm double-skin wall, 450mm wide.
Concrete volume follows directly: a 10m footing at 300 × 200mm is 10 × 0.3 × 0.2 = 0.6 m³. That is worth calculating alongside the block count, since it often turns out to be the larger material order.
Estimating time as well as materials
Block counts tell you what to buy. They also tell you roughly how long the job takes, which is the figure people forget to work out.
| Who | Blocks per day | 261-block wall |
|---|---|---|
| Experienced bricklayer | 200–300 | 1–1.5 days |
| Competent general builder | 120–180 | 1.5–2 days |
| Confident DIYer | 60–100 | 3–4 days |
| First-time DIYer | 30–60 | 4–8 days |
Those figures assume straightforward straight runs. Piers, openings and returns all slow things down considerably, and mixing your own mortar rather than having it delivered takes a meaningful bite out of laying time.
Common questions
How many blocks in a square metre?
Ten UK standard blocks (440 × 215mm) with a 10mm joint. US CMU works out at 12.5 per m², and EU 500 × 200mm blocks at 9.3.
How many bricks per square metre?
60 UK bricks per m² for a single skin in stretcher bond, including the mortar joint. US modular brick is around 72 per m².
How much wastage should I allow on blocks?
5% for a simple wall, 7 to 10% where there are several openings or returns. Aerated blocks chip easily so add a couple of percent more.
Do I subtract window and door openings?
Yes, but only the actual opening area. Don’t forget you’ll still need cut blocks around every opening, which is part of why wastage goes up when there are more of them.
How many blocks can one person lay in a day?
An experienced bricklayer lays 200 to 300 blocks a day on straightforward work. A competent DIYer should expect 60 to 100 while learning.