The American side is a different table, not a conversion
Switch market at the top and every figure changes. A British brick is 60 to the square metre. An American modular brick is 6.75 to the square foot, and converting the British number lands on 5.57, a fifth short. They are not the same brick in different units.
So the American path runs off Brick Industry Association Technical Notes 10 rather than off our metric arithmetic with a conversion bolted on. 675 modular brick and 5.5 cubic feet of mortar per 100 square feet at a 3/8 inch joint, a quarter more mortar at a half inch. Those tables already allow for bed and head joints in running bond, so recomputing them from the brick size would swap a measured industry figure for a worse one.
Concrete block is 1.125 a square foot whatever its thickness, and that is the counter-intuitive one. A CMU is nominally 8 by 16 on the face whether it is 6, 8 or 12 inches through, so the face coverage never changes. What changes is the mortar in the bed joint: about 2.3 cubic feet per 100 square feet at 6 inches, 3.0 at 8, and 4.5 at 12.
The output changes too. British practice batches cement, lime and sand to a ratio. American practice buys pre-blended masonry cement and adds sand, so the answer is bags and cubic feet rather than a mix to gauge, and which C270 type suits the job is an exposure question this tool leaves alone.
American brick is also usually a veneer over a backup rather than the outer leaf of a cavity wall, so the second wall behind it may be block, or it may be sheathing and studs. The tool warns when only brick has been entered, for the same reason the British side warns about a missing inner leaf: it is the half of the order people forget.
60 a square metre is not a magic number
It is arithmetic, and knowing where it comes from is what lets you get an unusual job right.
A standard UK brick is 215 × 102.5 × 65. Add a 10mm joint and it occupies 225 × 75 on the face, so a square metre holds 1000/225 × 1000/75 = 59.3 bricks. Blocks are 440 × 215, which with joints is 450 × 225, giving 9.88 a square metre.
Every other calculator hard-codes 60 and 10. This one derives them from the format size and the joint you set, which means a reclaimed imperial brick, a thin-joint aircrete wall or a 15mm joint on a rustic stock all still come out right instead of quietly returning the standard answer.
A cavity wall is two walls
Brick outside, block inside, and the same area twice. There are two ways people get that wrong and both cost real money:
- Counting the brick and forgetting the block behind it entirely.
- Counting the brick, then ordering blocks for the whole wall area again without realising it is the same wall.
So each leaf goes in as its own wall with its own unit. If you enter brick only on a wall of any size, the tool asks about the inner leaf rather than assuming you meant it.
The openings come off, per wall
On a house elevation the doors and windows are easily a fifth of the wall. That is a fifth of the order, and it is why openings are not an optional nicety.
They belong to the wall they are in rather than to the job, because a door in the front elevation is not a door in the gable, and getting a total right by accident is not the same as getting it right.
Type an opening bigger than its wall and the tool says exactly that, rather than telling you to put a wall in, which is what it did the first time, and is now a test.
Mortar out of the same sum
Most calculators work bricks one way and mortar another, using a coverage figure that came from somewhere else. Then the two answers disagree and nobody knows which to trust.
Here, mortar is the volume left when the units are taken out of the wall. Wall volume minus brick volume. Bed joints and perpends both fall out of that automatically, so the sand order and the brick order cannot contradict each other.
It also shows something people find surprising: blockwork uses roughly a third of the mortar brickwork does per square metre. If you are ordering sand for a job with both in it, that distinction is the difference between one bulk bag and three.
Waste, named rather than folded in
Five per cent covers breakages: the ones that arrive in pieces at the bottom of the pack, and the ones the forklift found.
Cuts and bond are a different thing. A wall thicker than half brick needs closers and half bats at every quoin and reveal, and those come out of whole bricks. The tool tells you when that applies instead of quietly padding the number, because an allowance you cannot see is an allowance you cannot argue with when a merchant quotes something different.
One thing worth knowing about running short: a second delivery is a different batch, and on a facing brick that is a visible colour change at whatever course you got to. It is the one shortage you cannot fix by going back to the merchant.
Thickness, ties and movement joints are design
It does not decide how thick your wall should be, how it should be tied, where the movement joints go or what it can carry. Those are design questions.
Next to it: mortar, sand and cement including what to actually put in the mixer, wall tie spacing, and concrete for the footings underneath.
Common questions
How many bricks per square foot?
For American modular brick at a 3/8 inch joint, 6.75 a square foot, or 675 per 100 square feet of wall. Those are Brick Industry Association figures from Technical Notes 10 Table 4 rather than our arithmetic, and the table already allows for bed and head joints in running bond. Norman brick is 450 per 100 square feet and utility brick 300, because the bigger the face the fewer you need.
How many concrete blocks do I need per square foot?
1.125, or 112.5 per 100 square feet, and here is the part that surprises people: it is the same figure for a 6, 8 or 12 inch block. A standard CMU is nominally 8 by 16 on the face whatever its thickness, so the face coverage never changes and only the bed joint gets wider. What does change with thickness is the mortar: roughly 2.3 cubic feet per 100 square feet for 6 inch block, 3.0 for 8 inch and 4.5 for 12 inch.
Why is a US brick 6.75 per square foot when a UK brick is 60 per square metre?
Because they are different objects rather than the same brick in different units. A British brick is 215 by 102.5 by 65 millimetres. An American modular brick is specified at 7 5/8 by 2 1/4 by 3 5/8 inches, nominally 8 by 2 2/3 by 4 with the joint included. Convert 60 per square metre and you get 5.57 per square foot, which is a fifth short of the real 6.75. That is why switching market here changes the whole table instead of converting the answer.
How many bricks per m2, and per square metre?
About 60 for a half-brick wall with a 10mm joint, and 120 for a one-brick wall. That figure is not a magic number: a standard brick is 215 × 65 on the face, so with joints it occupies 225 × 75, and a square metre holds 1000/225 × 1000/75 = 59.3. This tool derives it rather than hard-coding it, so a non-standard brick or a different joint still gives a right answer.
How many concrete blocks are in a square metre?
Just under 10. A 440 × 215 block with a 10mm joint occupies 450 × 225, giving 9.88 per square metre. Same face size for 100mm, 140mm and 215mm blocks, so the count per square metre is the same and only the mortar volume changes.
Why does it want me to add two walls for a cavity wall?
Because a cavity wall is two leaves and they are different materials. Entering them separately makes it hard to do the two things people actually do wrong: count the brick and forget the block behind it, or order blocks for the whole area having already counted the brick. If you only enter brick on a wall of any size, the tool asks about the inner leaf.
Do I need to take the windows off?
Yes, and it matters more than people expect. On a house elevation the doors and windows are easily a fifth of the wall area, which is a fifth of the order. Openings hang off the wall they are in rather than off the job, because a door in the front is not a door in the gable.
Where does the mortar figure come from?
The same sum as the bricks. Mortar is the volume left when you take the units out of the wall, so the bed joints and perpends both fall out of it automatically. That is why the sand order and the brick order agree with each other here rather than being two separate guesses with two separate roundings.
How much waste should I allow?
Five per cent covers breakages and the ones at the bottom of the pack that arrive in pieces. A bond thicker than half brick needs closers and half bats at every quoin and reveal, and those come out of whole bricks, so allow a bit more: the tool says so rather than quietly inflating the figure.