How many paving slabs do I need per square metre?

It depends on slab size. For 600x600mm slabs with 10mm joints you need approximately 2.7 slabs per m². For 450x450mm slabs you need about 4.7 per m². Always add 10% for cutting waste and breakages.

How thick should the sand bed be for paving slabs?

A mortar bed of 25-40mm is standard for patio slabs on a compacted sub-base. Use a 4:1 sharp sand to cement mix. For lighter-use paths, a 25mm bed is sufficient; for driveways and heavy-traffic areas, use 30-40mm.

What sub-base depth do I need for a patio?

A minimum of 100mm compacted Type 1 MOT sub-base is recommended for patios. For driveways or areas with vehicle access, increase to 150-200mm. The sub-base should be compacted in layers using a plate compactor.

Do I need edge restraint for patio paving?

Yes. Edge restraint prevents slabs from shifting outward over time. Options include concrete haunching, aluminium or plastic edge restraints, or a brick/block border. Allow for the full perimeter of the paved area.

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Patio Paving Calculator — Slabs, Sand & Cement

Calculate paving slabs, sand, cement and sub-base quantities for your patio project.

Patio Length

Longest dimension of the area

Patio Width

Shortest dimension of the area

Slab Size

Joint Width

Gap between slabs

Laying Pattern

Pattern affects wastage due to cuts at edges

How We Calculate This

This calculator works out the number of paving slabs needed based on your patio dimensions, chosen slab size, joint width and laying pattern. It also estimates sand, cement and sub-base quantities.

The calculation

Effective slab area = (slab width + joint) × (slab height + joint)
Base slabs = patio area ÷ effective slab area
Pattern wastage is added for herringbone (+10%) or stretcher bond (+5%)
User-defined wastage percentage is added on top
Sand estimated at 50 kg/m² for a 25mm mortar bed
Cement at 1 bag (25 kg) per 4 m² for a 4:1 mix

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.