UK concrete block
440.0 × 215.0 × 100.0 mm
17.32 × 8.46 × 3.94 in · format 450.0 × 225.0 mm · 10 per m² · United Kingdom
About this unit
The standard British block. Its format is 450 × 225 — and 225 is exactly three brick courses, which is the whole point: blockwork and brickwork rise together, so a cavity wall can be built with brick outside and block inside and meet at every third course.
The size that matters is the format
A block is never laid on its own. Add one 10.0 mm joint and the working unit becomes 450.0 × 225.0 mm, and every dimension in the wall is a multiple of that rather than of the block.
| Actual size | 440.0 × 215.0 × 100.0 mm |
| Mortar joint | 10.0 mm |
| Format size | 450.0 × 225.0 mm |
| Per square metre, single skin | 9.88 — order 11 with 5% waste |
| Courses per metre of height | 4.44 |
| Units per metre of length | 2.22 |
Setting out
Ten courses rise 2250 mm and ten units run 4500 mm. Openings, sills and damp courses are placed on those multiples wherever possible, because a wall that has to be cut to reach a dimension costs labour and shows.
Other United Kingdom units
| Unit | Actual | Format | Per m² |
|---|---|---|---|
| UK standard brick | 215 × 65 × 103 mm | 225.0 × 75.0 | 59.3 |
| UK imperial brick | 228 × 68 × 108 mm | 238.0 × 78.0 | 53.9 |
| UK metric modular | 200 × 75 × 100 mm | 210.0 × 85.0 | 56.0 |
Frequently asked questions
What size is a uk concrete block?
440.0 × 215.0 × 100.0 mm (17.32 × 8.46 × 3.94 in). Add the 10.0 mm joint and the working size — the format — is 450.0 × 225.0 mm.
How many blocks per square metre?
9.9 for a single skin — 10 in practice, before allowing for breakage. That comes straight from the format: 1,000,000 mm² ÷ (450.0 × 225.0) = 9.88.
How many courses per metre of height?
4.44 courses, at 225.0 mm each. Setting out from a fixed course height is why a window head or a damp course lands where it does rather than where a drawing might prefer.
Why does the joint matter so much?
Because the block on its own is never the unit of construction. Masonry is set out on the format size — one unit plus one joint — and every dimension in a wall is a multiple of it. A 215.0 mm block with a 10.0 mm bed rises 225.0 mm per course, and that 225.0 is the number the wall is actually built from.