US concrete block
396.9 × 193.7 × 193.7 mm
15 5/8 × 7 5/8 × 7 5/8 in · format 406.4 × 203.2 mm · 13 per m² · North America
About this unit
The standard American CMU, nominally 8 × 8 × 16 inches once the joint is counted. Two block courses equal three modular brick courses at 16 inches, which is the same coursing trick the British block plays.
The size that matters is the format
A block is never laid on its own. Add one 9.5 mm joint and the working unit becomes 406.4 × 203.2 mm, and every dimension in the wall is a multiple of that rather than of the block.
| Actual size | 396.9 × 193.7 × 193.7 mm |
| Mortar joint | 9.5 mm |
| Format size | 406.4 × 203.2 mm |
| Per square metre, single skin | 12.11 — order 13 with 5% waste |
| Courses per metre of height | 4.92 |
| Units per metre of length | 2.46 |
Setting out
Ten courses rise 2032 mm and ten units run 4064 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 North America units
| Unit | Actual | Format | Per m² |
|---|---|---|---|
| US modular brick | 194 × 57 × 92 mm | 203.2 × 66.7 | 73.8 |
| US queen brick | 194 × 70 × 79 mm | 203.2 × 79.4 | 62.0 |
| US king brick | 244 × 70 × 76 mm | 254.0 × 79.4 | 49.6 |
| US utility brick | 295 × 92 × 92 mm | 304.8 × 101.6 | 32.3 |
Frequently asked questions
What size is a us concrete block?
396.9 × 193.7 × 193.7 mm (15 5/8 × 7 5/8 × 7 5/8 in). Add the 9.5 mm joint and the working size — the format — is 406.4 × 203.2 mm.
How many blocks per square metre?
12.1 for a single skin — 13 in practice, before allowing for breakage. That comes straight from the format: 1,000,000 mm² ÷ (406.4 × 203.2) = 12.11.
How many courses per metre of height?
4.92 courses, at 203.2 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 193.7 mm block with a 9.5 mm bed rises 203.2 mm per course, and that 203.2 is the number the wall is actually built from.