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How the brick calculator works
A brick counts as more than the brick itself, because the mortar joint around it occupies wall as well. The calculator works on the module: the brick length plus the joint, multiplied by the brick height plus the joint. A standard 215 × 65 mm brick with a 10 mm joint occupies 225 × 75 mm of wall face, which is 0.016875 m² — so one square metre of single-skin wall takes 59.26 bricks. That is the well-known "60 bricks per square metre" figure, arrived at properly rather than rounded.
Change any one of those numbers and the count moves with it. A 215 × 73 mm brick laid with a 10 mm joint needs 55 per m², and the same brick with a fat 15 mm joint needs 51. That is why the calculator asks for the brick size and the joint instead of a single rate — it matters most when you are pricing a wall in an expensive facing brick.
Single skin, double skin and blockwork
Single skin is one leaf, roughly 100 mm thick, and it is what a garden wall, a shed base or a dwarf wall under a conservatory usually is. Double skin is two leaves — either a cavity wall or a solid one-brick wall 215 mm thick — and it takes twice the bricks and twice the mortar for the same face area. The two leaves are tied together with wall ties at about 2.5 per m², and a cavity wall also wants a damp-proof course and weep vents.
Blockwork is the faster, cheaper option behind the scenes: a 440 × 215 mm block covers more than ten times the face of a brick, so the same 20 m² wall needs 208 blocks instead of 1,245 bricks. Blocks use far less mortar too — about 0.0007 m³ each against 0.0003 m³ for a brick — because there are fewer joints to fill per square metre.
Mortar, sand and cement
Mortar volume is derived geometrically: the module cell the brick sits in, minus the brick. That gives roughly 0.0003 m³ per brick and 0.0007 m³ per block with a 10 mm joint, which matches the trade rule of thumb. Because sand and cement are bought dry and mixed with water, the wet volume is multiplied by 1.33 to get the dry volume you actually order, then split by the mix ratio. A 1 : 5 mix means one part cement to five parts sand, so a sixth of the dry volume is cement and five sixths is building sand.
Two practical notes. Keep the joint consistent — a wall built with alternating fat and thin joints is weaker and looks wrong from the road. And never mix mortar stronger than the units it holds: a 1 : 3 mix against a soft brick will crack the brick faces and leave the wall looking shabby within a winter or two.
Brick FAQs
How many bricks do I need for a 10 m × 2 m wall?
1,245 bricks for a single skin, using 215 × 65 mm bricks with 10 mm joints and the default 5% waste: 20 m² × 59.26 bricks per m² is 1,185, plus 5% for cuts and breakages. Double the area, or double the skin, and the figure is about 2,490.
How many bricks per square metre?
60 bricks per m² for a standard 215 × 65 mm brick with a 10 mm joint in single-skin work — 59.26 exactly, before waste. A 73 mm-high brick needs 55 per m², and blocks need about 10 per m² because each one covers 440 × 215 mm.
How much mortar does a brick wall need?
Roughly 0.0003 m³ per brick, or 0.3 m³ for every 1,000 bricks, at a 10 mm joint. For a 20 m² single-skin wall that is about 0.37 m³ of wet mortar, which works out at five 25 kg bags of cement and 27 bags of building sand in a 1 : 5 mix. Buy the sand in a bulk bag if the wall is any size at all — it is far cheaper per tonne.
What mix should I use for a garden wall?
1 : 5 cement to building sand is the general-purpose mix and the one to use above the damp-proof course for most bricks. Go stronger (1 : 4) below ground or for a retaining wall, and weaker (1 : 6) with soft or highly absorbent bricks. Adding a plasticiser or hydrated lime makes the mortar easier to spread and helps it grip.
How many bricks are in a pack?
UK merchants usually sell in packs of 500, though some facing bricks come in 400s or 560s and pack sizes vary by manufacturer. Check the pack size before ordering: if the calculator says 1,245 bricks and packs hold 500, you need three packs and will have around 255 spare — which is fine, because a matching brick from the same batch is worth having for repairs.
Do I need a damp-proof course?
Yes, on any wall that meets the ground. A 100 mm DPC laid at least 150 mm above ground level stops moisture wicking up through the brickwork, which is what causes the white salt bloom and the spalling faces you see on old garden walls. Measure it along the wall length — the calculator shows the figure you need.