GardenCalcs.uk
Patio Area Calculator
Work out patio area, perimeter, slabs, sub-base and bedding mortar for rectangular or L-shaped patios.
Patio length in metres (the longest side of the bounding rectangle)
Patio width in metres
Rectangular for a square or rectangle patio; L-shaped for an L footprint (a corner notch removed)
Nominal slab size — coverage includes a 10 mm joint
For an L-shape only: the share of the bounding rectangle the patio covers (100% = full rectangle; 75% leaves a quarter-corner notch)
Extra slabs for cuts and breakages — 10% for concrete or sandstone, ~15% for porcelain or many angled cuts
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 ≈ 2.7 slabs/m², 450×450 mm ≈ 4.7 slabs/m².
Frequently Asked Questions
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 0.37 m², so about 2.7 slabs per m². Sub-base is MOT Type 1 at 100 mm compacted depth (~2.0 t/m³); bedding mortar is a 40 mm full bed.
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.
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.
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.
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.
Related Calculators
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Calculate how many paving slabs you need for a patio or path.
Block Paving Calculator
Calculate block paving quantities with wastage allowance.
Jointing Sand Calculator
Calculate kiln-dried or polymeric jointing sand for paving joints.
Resin Bound Gravel Calculator
Calculate resin and aggregate quantities for resin-bound surfaces.
Gravel Calculator
Work out gravel quantities in tonnes or bulk bags for drives and paths.
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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.