How Many Paving Slabs for a Patio?
Quick Answer
You need approximately 35 paving slabs
Based on: 4m x 3m patio, 600 x 600mm slabs, 10mm joints, 5% wastage allowance
How We Calculated This
The most popular patio slab size in the UK is 600mm x 600mm. With a 10mm joint between slabs, each slab occupies an area of 610mm x 610mm = 0.3721m².
- Patio area: 4m x 3m = 12m²
- Slabs needed (no wastage): 12 ÷ 0.3721 = 32.2, round up to 33 slabs
- With 5% wastage: 33 x 1.05 = 34.65, round up to 35 slabs
Why Only 5% Wastage?
Paving slabs are laid in a regular grid pattern with minimal cuts needed (usually only at the edges). A 5% wastage allowance is standard for rectangular patios. Increase to 10% if you have an irregular shape, angled edges, or a multi-size random layout.
Common UK Paving Slab Sizes
- 600 x 600mm: ~2.8 slabs/m² — most popular size
- 450 x 450mm: ~4.7 slabs/m²
- 600 x 300mm: ~5.3 slabs/m²
- 900 x 600mm: ~1.8 slabs/m²
Laying Materials
Slabs should be laid on a full mortar bed over a compacted sub-base. For a 4m x 3m patio you will need:
- Sub-base (Type 1 MOT): 12m² x 0.1m = 1.2m³ = ~2.16 tonnes
- Sharp sand (bedding layer): 12m² x 0.03m = 0.36m³ = ~0.6 tonnes
- Cement (for mortar bed, 1:4 mix): ~4 bags of 25kg
- Jointing compound or kiln-dried sand: 1–2 bags
Full Mortar Bed vs Spot Bedding
Always lay patio slabs on a full mortar bed rather than the five-spot method. Spot bedding can lead to slabs rocking, cracking under load, and water pooling underneath. A full bed of semi-dry mortar (1 part cement to 4 parts sharp sand) gives far better support and a longer-lasting result.
Tips
Set a fall of 1 in 60 (about 17mm per metre) away from the house to ensure rainwater drains properly. Use a string line and spirit level across every row. Stagger joints in a brick-bond pattern for a stronger result if using rectangular slabs.