About this calculator
Count M140 and M190 concrete blocks for garden walls, foundation walls, garages and extensions, along with the mortar to lay them.
How it’s calculated
M140 (390 × 140 × 190 mm) and M190 (390 × 190 × 190 mm) blocks with 10 mm joints cover 400 × 200 mm each, which works out to 12.5 blocks per m², the figure block makers quote. Blocks = net wall area × blocks per unit area, plus waste.
Worked example
With these inputs:
- Wall length
- 10 m
- Wall height
- 2.4 m
- Openings area
- 0 m²
- Block
- M140, 390 × 140 × 190 mm
- Mortar mix (cement:sand)
- Class II, common cement (normal load-bearing walls)
- Waste allowance
- 5%
the result is:
- Blocks needed
- 315 blocks
- Wall area (net)
- 24 m²
- Courses
- 12
- Mortar
- Class II, common cement (normal load-bearing walls)
- Cement (50 kg bags)
- 3 bags
Tips from the trade
- Subtract openings, but add back for lintel bearings and cut blocks at the ends.
- Order a few extra half-blocks or cutters for corners and ends.
- Mortar figures assume normal 10 mm joints and include a practical allowance for droppings.
Common questions
How many blocks per square metre?
12.5 M140 or M190 blocks per m² with 10 mm joints.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.