Question 1

How do I work out how many patio slabs I need?

Accepted Answer

Divide your patio area by the effective area of each slab (slab size plus joint gap on each side). Then add your wastage allowance for cuts and breakages - 10% is typical. This calculator does all that for you - just enter patio dimensions, slab size and joint gap.

Question 2

What joint gap should I use for patio slabs?

Accepted Answer

For most domestic patios, a joint gap of 10–15mm is common with mortar pointing. For dry-laid patios with polymeric sand, a smaller gap of 3–8mm may be used. Check the manufacturer's recommendation for the specific slab and jointing product you are using.

Question 3

How much wastage should I allow for patio slabs?

Accepted Answer

10% is a standard starting point for a straightforward rectangular patio. For irregular shapes, curves or complex patterns that require more cutting, 15–20% is more appropriate. Always buy from the same batch - matching colour and texture after the fact is difficult.

Question 4

What are the most common patio slab sizes in the UK?

Accepted Answer

Common UK patio slab sizes include 600×600mm, 600×450mm, 600×300mm and 450×450mm. Larger format slabs (900×600mm and above) are increasingly popular. Our calculator works with any size - just enter your slab dimensions.

Question 5

Do I need to include the sub-base in this calculator?

Accepted Answer

No - this calculator works out slab quantities only. For your sub-base, use our MOT Type 1 Calculator or Sub Base Calculator. For gravel bedding layers, use the Aggregate Calculator.

Slab size	Coverage per slab	Notes
600×600mm	0.36 m²	Most common UK patio slab
600×450mm	0.27 m²	Popular rectangular format
450×450mm	0.2025 m²	Classic square format
900×600mm	0.54 m²	Large format - fewer joints
600×300mm	0.18 m²	Long narrow - decorative

Patio Slab Calculator UK

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Patio slab estimate

Common UK patio slab sizes

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