Ten blocks to the square metre, and the reason that number works is that it already includes the mortar joint. The count is the easy part — the thing that decides how the day goes is what each block weighs.
Enter the wall area and the coordinating block size — block plus one joint. Defaults are the UK standard 440 × 215.
Works in metric and US imperial — you choose at the start and can switch at any time. Every figure this calculator uses is published with its source, and the result comes with a printable order sheet. No account, no email, and nothing you type leaves your browser.
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Because the number already includes the mortar joint. The coordinating size of a standard UK block is 450 × 225 mm — a 440 × 215 block plus a 10 mm joint — which gives 9.88 blocks per square metre. Everyone rounds it to ten. Enter the coordinating size rather than the bare block size, or the count comes out several per cent high.
The count is the easy part; what decides how the day goes is what each block weighs. The difference between aircrete and dense concrete block is more than double, for exactly the same wall. That changes who can lay it, how fast it goes up, and whether the pack can be moved by hand. It is worth asking the merchant for the weight per block rather than discovering it on delivery.
Do not lay blocks in the rain and do not lay wet blocks. Aircrete in particular soaks up water, and a saturated block shrinks as it dries and cracks the wall — keep the packs sheeted. Blockwork also shrinks in long runs: anything over about 6 m generally wants a vertical movement joint, and where it goes should be decided before you start rather than after the first crack appears.
9.88 for a standard UK block at the coordinating size of 450 by 225 mm, which the trade rounds to ten. The figure works because the coordinating size already includes the 10 mm mortar joint.
The block plus one mortar joint — 450 by 225 mm for a standard 440 by 215 block with a 10 mm joint. Enter the coordinating size, not the bare block size, or you will over-order by several per cent.
In runs over about 6 m, generally yes. Blockwork shrinks, and a vertical movement joint decides where that movement is accommodated. Decide the position before you start building.
Aircrete cuts cleanly with a handsaw, which is better. Dense blocks need a disc cutter, and the dust is a genuine hazard — wet-cut and wear proper protection.