How many paving slabs per m²?

It depends on the slab size: 600x600mm slabs = approximately 2.8 per m² (with 10mm joints), 450x450mm = approximately 4.7 per m², 400x400mm = approximately 5.9 per m², and 600x300mm = approximately 5.4 per m². This paving slab quantity calculator works out the exact number including wastage. For indoor floor tiles, see our Floor Tile Calculator (/flooring/floor-tile-calculator).

How thick should the sand bed be for paving?

The sharp sand laying bed (also called the bedding layer) should be 30-50mm thick (compacted) on top of your sub-base. We use 50mm as standard. This provides a level surface to lay slabs onto. Use sharp sand (not building sand) — it compacts better and provides better drainage.

What is the best joint size for paving slabs?

A 10mm joint (also called a gap or spacing) is standard for most paving slabs in the UK. This allows room for pointing with mortar (4:1 sand:cement mix) or kiln-dried sand. Wider joints of 15mm may be used with natural stone. Too narrow and pointing becomes difficult; too wide and it looks uneven.

Should I use mortar or sand to point paving?

Mortar pointing (4:1 sharp sand to cement) is the most durable option for patios and high-traffic areas. Brush-in kiln-dried sand is quicker but less durable and can wash out. Resin-based jointing compound is a modern alternative that sets hard but remains slightly flexible. Ensure your patio has the correct drainage fall — use our Drainage Fall Calculator (/landscaping/drainage-fall-calculator).

Do I need a sub-base under paving slabs?

Yes — always lay paving on a proper sub-base. Use 100mm of compacted Type 1 MOT sub-base for pedestrian areas, or 150mm for driveways — our Type 1 Sub-Base Calculator (/landscaping/type-1-sub-base-calculator) works out quantities. The sub-base goes down first, then 50mm of sharp sand, then the slabs. For a gravel surface instead, see our Gravel Calculator (/landscaping/gravel-calculator).

TradeCalcs

Paving Slab Calculator — Slabs, Sand & Cement

Calculate how many paving slabs you need plus sand for the laying bed and cement for pointing. Standard UK slab sizes.

Area Length

Length of the area to pave

Area Width

Width of the area to pave

Slab Size

600×600mm is the most popular size

Include wastage allowance

Adds 10% extra for cuts and breakages

Wastage Percentage

10% standard, 15% for complex layouts

Price Per Slab (optional)

Enter your supplier price for a cost estimate

How We Calculate This

Our paving slab calculator works by dividing your total area by the area covered by each slab (including joint gaps) to determine the number of slabs needed.

The formula

Slabs across = Area length ÷ (Slab width + Joint width)

Slabs down = Area width ÷ (Slab height + Joint width)

Total slabs = Slabs across × Slabs down × Wastage factor

Sand and cement calculations

Sharp sand bed: Area × 50mm depth × 1.6 t/m³ density
Pointing cement: ~3 kg per m² (based on 4:1 sand:cement mortar)
Joint width: 10mm standard

Wastage

We recommend 10% wastage for rectangular areas. For areas with lots of cuts (curves, angles), increase to 15%. Paving slabs can break during cutting and handling, so always order extra.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.