How Many Concrete Blocks Do I Need? Per m² and by Wall Size (UK)
A standard 440 × 215 mm concrete block (with its 10 mm joints) covers 0.1 m² of wall, so a wall needs 10 blocks per square metre. A wall 5 m long and 2 m high (10 m²) needs 104 blocks with 5% waste, plus about 0.08 m³ of mortar. The concrete block calculator works out the blocks, the cement and the sand for your wall.
Blocks and mortar by wall size
100 mm blocks, 1:5 mortar, 5% waste:
| Wall | Area | Blocks to order | Wet mortar | Bags of cement (25 kg) |
|---|---|---|---|---|
| 3 × 1.2 m | 3.6 m² | 38 | 0.03 m³ | 1 |
| 5 × 2 m | 10.0 m² | 104 | 0.08 m³ | 2 |
| 6 × 2.4 m | 14.4 m² | 150 | 0.12 m³ | 2 |
| 10 × 2.4 m | 24.0 m² | 249 | 0.20 m³ | 3 |
| 15 × 3 m | 45.0 m² | 467 | 0.37 m³ | 5 |
| 20 × 3 m | 60.0 m² | 623 | 0.49 m³ | 7 |
Block sizes
| Thickness | Typical use |
|---|---|
| 100 mm | Internal partitions and non-loadbearing walls |
| 140 mm | Loadbearing inner leaf, internal walls |
| 190 mm | Loadbearing walls, retaining walls |
| 215 mm | Boundary and retaining walls |
All have a standard face of 440 × 215 mm, so the count per square metre is the same: only the thickness (and the weight) changes.
Before you build
- A wall needs a proper foundation, on firm ground and deep enough to be clear of frost. The concrete for it is separate: see the concrete calculator.
- Dampproof courses, wall ties and movement joints matter as much as the blocks. Follow the drawings and Building Regulations.
- Keep blocks off the ground and covered, and do not lay them in frost or heavy rain.
- Use a line and a level for each course, and check the first course carefully, since the rest follows it.
- Order a few spare blocks, and mix mortar in small batches.
Estimates only: follow the plans and your building control.
Frequently asked questions
How many concrete blocks per square metre?
Ten blocks of 440 × 215 mm per square metre of wall, including a 10 mm joint. A wall 5 × 2 m (10 m²) needs 99 blocks, or 104 with 5% waste.
How many blocks for a wall 10 m long and 2.4 m high?
249 blocks of 100 mm with 5% waste, for 24 m² of wall.
How much mortar does blockwork need?
About 0.08 m³ of wet mortar for 10 m² of wall: 2 bags of cement (25 kg) and 0.14 tonnes of building sand at a 5:1 mix.
What thickness of block should I use?
100 mm blocks suit internal and non-loadbearing walls, 140 mm and 190 mm blocks suit loadbearing walls, and 215 mm for retaining and boundary walls. Check the design with your building control or engineer.
What mortar mix for blockwork?
A common mix is 1 part cement to 5 or 6 parts building sand, with a plasticiser. The calculator offers 4, 5 and 6 parts.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.