How it works
Every machine cut stone shows an 18 × 9 inch face on the wall. With a 10 mm mortar joint each stone covers about 0.111 m², so a square metre of wall takes about 9 stones, whatever the thickness. The thickness (4", 6" or 9") only decides which stone you buy: 9" for outside and load-bearing walls, 6" for most partitions, 4" for light partitions.
Step by step
- Measure the wall length and height in metres and multiply them for the wall area.
- Subtract the area of every door and window.
- Divide the net area by 0.1115 m², the face of one 18 × 9 inch stone with a 10 mm joint.
- Add 5–10% for breakage and cutting, then round up to whole stones.
Worked example
A 10 m wall, 3 m high, with one door (1.9 m²) and two windows (2 × 1.44 m²): net area 30 − 4.78 = 25.2 m². 25.2 ÷ 0.1115 = 226 stones, plus 5% for breakage = 238 stones. Mortar: 238 ÷ 50 ≈ 5 bags of cement and about 1 tonne of sand.
Questions
How many machine cut stones are in one square metre?
About 9 stones per m² of wall with a 10 mm joint, for 4", 6" and 9" stones alike (they share the same 18 × 9 inch face).
How much wastage should I allow?
Allow 5% for breakage and cutting on a straight wall, and up to 10% where there are many corners and openings.
Which stone size should I use?
Use 9" stones for outside and load-bearing walls and 6" stones for most internal walls. Your engineer or fundi confirms the right size for your plan.