Paving slab calculator
Enter the patio size and slab size. You’ll get the slab count plus the sub-base and bedding layers underneath.
Measuring in feet and inches? Use the US version
Slabs needed
46 slabs
- Sub-base
- 1.6 m³ (about 3.2 tonnes)
- Bedding
- 0.64 m³
- Patio area
- 16 m²
- Slabs per m²
- 2.69 including joints
How it works
Each slab effectively covers its own size plus one joint in each direction. The calculator divides the patio area by that, adds your allowance for cuts and rounds up. The sub-base and bedding are area × depth. The tonnage for the sub-base assumes about 2 tonnes per cubic metre, a typical figure for crushed stone once compacted.
Example
With patio length 4 m, patio width 4 m, slab length 600 mm, slab width 600 mm, joint width 10 mm, extra for cuts 5%, sub-base depth 100 mm, bedding depth 40 mm, the answer is 46 slabs.
Tips before you buy
- A compacted sub-base of about 100 mm suits most garden patios. Soft or clay ground needs more.
- Give the patio a gentle fall away from the house so rainwater runs off, roughly 1 in 60 to 1 in 80.
- Buy a few spare slabs. Natural stone varies between batches, so later matches are hard.
Common questions
How many 600 × 600 slabs per square metre?
2.78 without joints, or about 2.69 allowing for 10 mm joints.
How many slabs for a 4 × 4 m patio?
With 600 × 600 slabs and 10 mm joints, 46 slabs including 5% extra.
How deep should a patio sub-base be?
About 100 mm of compacted crushed stone for a typical garden patio, more on soft ground.