Paving calculator
Enter the patio area in m², pick a slab size and joint width, and see how many slabs and how much Type 1 sub-base to order.
For sand and other materials, use the aggregate calculator.
Estimates only. Check the manufacturer's coverage rates.
How this is calculated
Slabs are counted from the area each slab covers including its joint: (slab length + joint) x (slab width + joint). A 600 x 600 mm slab with a 10 mm joint covers 0.3721 m², so 12 m² with 5% wastage needs 34 slabs. The count is rounded up.
The sub-base estimate is the area x the sub-base depth, with an extra allowance for compaction: volume (m³) = area (m²) x depth (mm) / 1000 x (1 + extra / 100). Tonnes assume a Type 1 approximate bulk density of 2.1 tonnes per m³, shown here as an assumption.
Patios need a compacted sub-base and a bed for the slabs. This page estimates slabs and sub-base only; use the aggregate calculator for sand and other materials.
The wastage allowance, 5% by default, covers cuts and breakages around edges and corners. Keep a few spare slabs from the same batch for future repairs.
- 2.1 tonnes per m³ is an approximate Type 1 bulk density, shown as an assumption.
- This page estimates slabs and sub-base only; use the aggregate calculator for sand and other materials.
- Keep a few spare slabs from the same batch.
Frequently asked questions
How many 600 x 600 slabs per m²?
About 2.69 with a 10 mm joint, since each slab plus its joint covers 0.3721 m².
How much sub-base do I need?
Area x depth gives the volume; the calculator adds 10% extra by default and converts to tonnes at 2.1 tonnes per m³, an approximate Type 1 bulk density shown as an assumption.
Does this include the bedding sand?
No. This page estimates slabs and sub-base only. Use the aggregate calculator for sand and other materials.