How is this calculated?

Area = length × width (an L-shape uses the fill fraction of its bounding rectangle). Slabs = ceil(area ÷ slab footprint × wastage); a 600×600 mm slab with a 10 mm joint covers 0.36 m², so about 2.78 slabs per m². Sub-base is MOT Type 1 at 100 mm compacted depth (~1.6 t/m³); bedding mortar is a 40 mm full bed.

Should I add extra for wastage?

Yes. The default 10% allowance covers cuts, breakages and spillage for sandstone or concrete slabs — increase it to about 15% for porcelain or for a patio with many angled cuts.

How deep should the sub-base be?

For a foot-traffic garden patio, lay 100 mm of compacted MOT Type 1 (this calculator assumes 100 mm). A driveway or load-bearing surface needs 150 mm or more.

What is the ideal patio size?

Allow 3-4 m² per person for comfortable dining. A family of four needs about 12-16 m². Standard sizes are 3×3 m, 4×3 m, or 4×4 m.

Does a patio need a slight slope for drainage?

Yes, a minimum fall of 1:80 (12.5 mm per metre) away from the house is essential. This ensures rainwater drains away and does not pool against walls.

GardenCalcs

Patio Area Calculator

Work out patio area, perimeter, slabs, sub-base and bedding mortar for rectangular or L-shaped patios.

Length

Patio length in metres (the longest side of the bounding rectangle)

Width

Patio width in metres

ShapeRectangular for a square or rectangle patio; L-shaped for an L footprint (a corner notch removed)

Slab SizeNominal slab size — coverage includes a 10 mm joint

How We Calculate This

Enter the patio length, width and slab size. The calculator works out the area and perimeter, then estimates the paving slabs (with a 10% wastage allowance by default), the MOT Type 1 sub-base at 100 mm compacted depth, and the sharp-sand-and-cement bedding mortar for a 40 mm full bed. Slab coverage uses the nominal footprint including a 10 mm joint: 600×600 mm ≈ 2.78 slabs/m², 450×450 mm ≈ 4.7 slabs/m².

Frequently Asked Questions

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Last updated: June 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.