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Patio Build-Up Calculator

Slabs, sub-base, bedding, jointing, edging and excavation for any patio.

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Inputs
Got a bay window or conservatory? Set it out in Setting Out & Levels → Bays & conservatories. It carves the bay footprint out of the paved area and adjusts the wall run, then hands the corrected figures back here.

Pick a stock size or choose Custom to enter your own.

Pick the drainage detail along the house wall. A shingle strip is the minimum good-practice detail; a dry channel or land drain stops the slabs a course short and adds gravel, geotextile and pipe to the take-off.

19 advanced inputs hidden. Switch to Advanced to fine-tune.

Site context (optional)

Helps tailor algae, weather and longevity advice.

Confidencehigh· 91Complexitymedium· 42
Slabs required
36

Order what you need for this job

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Based on 600×600mm slabs, 5mm joints, 8% total allowance (5% waste + 3% cuts)

Heads-up: You're on a single-size layout, so every slab is the same dimension. The same material is sold in several sizes (600×600, 900×600, 800×800, 1200×600…). Why it matters: Larger slabs mean fewer pieces but heavier lifts and more cut waste — switch the Slab size above to match what your supplier actually stocks before ordering.

Drainage & falls

Surface drainage is advised here — set a gentle fall away from the house and any structures.

Lay paving with falls of 1:80 (recommended) or 1:60 (minimum) away from buildings.

Why it matters: Smooth paving needs a positive fall to overcome surface tension and shed water before it ponds in low spots.

If ignored: Insufficient falls cause standing water, algae growth, freeze-thaw damage and water tracking back toward the building.

  • • Recommended falls: 1:80
  • • Falls 1:80 minimum
  • • Surface water must drain to a permeable area or drain

Quantities pre-filled from your calculation (15.0 m²). Partner links — we may earn a small commission if you buy, at no cost to you.

Essentials for this job

Quantities include a ~10% waste allowance. Guide prices are indicative UK ranges (materials only, inc. VAT) — always confirm with the supplier before ordering.

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This app provides general UK guidance and material estimates only. It is not legal, planning, engineering or building-control advice. Always confirm requirements with your local planning authority, building control, utility providers, manufacturers or qualified professionals.

Worked example

A 6.0 m × 4.0 m porcelain patio in 600 × 600 slabs, stretcher bond, dug out of an existing lawn.

Inputs

Paving material
Porcelain
Area
6.0 m × 4.0 m
Slab size
600 × 600 mm, 20 mm thick
Pattern
Stretcher bond, 5 mm joints
Build-up
100 mm sub-base, 40 mm bedding
Step by step calculation for this example
StepWorkingResult
Area6.0 m × 4.0 m24 m²
Total allowancebreakage waste plus cutting allowance8 %
Slabs24 m² ÷ 0.366 m² per slab (incl. joints), plus the allowance71
Sub-base24 m² × 0.10 m compacted, at 2.1 t/m³, plus 10%6.93 t
Bedding mortar24 m² × 0.04 m of 6:1 sand and cement2.02 t
Excavation24 m² × 0.16 m dig, bulked by 30%6.14 t
What to order for this example
What to orderQuantity
Slabs required71
MOT Type 1 (order qty incl. 10%)6.93 t
Mortar bed2.02 t
Slurry primer36 kg
Jointing compound84 kg
Spoil tonnes6.14 t

In short: Order 71 slabs, 6.93 t of MOT Type 1, 2.02 t of bedding mortar, 36 kg of slurry primer and 84 kg of jointing compound.