UkToolCalc.uk
  1. Home
  2. Concrete, Sub-Base & Paving
  3. Patio & Paving Slab Calculator
  4. How many patio slabs do I need?
Quick answer

How Many Patio Slabs Do I Need?

600 × 600mm slabs with 10mm joints and 10% for cuts, on 100mm of MOT Type 1 and a 40mm full mortar bed (6:1 sharp sand and cement).

Page last reviewed 26 October 2026 by the UkToolCalc team

A 4 × 3m patio needs 36 slabs of 600 × 600mm (or 24 of 900 × 600mm), plus 4 bulk bags of MOT Type 1, 2 of sharp sand and 6 bags of cement for the bed.

Work out your own in the Patio & Paving Slab calculator
  • ~2.7600 × 600 slabs per m²
  • +10%for cuts and breakages
  • 100mmMOT Type 1 under the bed
  • 1:60fall away from the house

Slabs and base materials by patio size

600 × 600mm slabs, 10mm joints, 10% for cuts, 850kg bulk bags.

PatioAreaSlabsMOT Type 1Sharp sandCement
3 × 3 m9 m²271.98 t (3 bags)0.72 t (1 bag)5 bags
4 × 3 m12 m²362.65 t (4 bags)0.96 t (2 bags)6 bags
5 × 4 m20 m²604.41 t (6 bags)1.61 t (2 bags)10 bags
6 × 4 m24 m²715.29 t (7 bags)1.93 t (3 bags)12 bags

With 900 × 600mm slabs, a 4 × 3m patio takes 24 instead of 36. The base materials stay the same.

The sum

Slabs = area × 1.1 ÷ ((slab length + joint) × (slab width + joint)) 4 × 3m: 12 × 1.1 ÷ (0.61 × 0.61) = 36

The patio calculator also works out jointing compound and costs. The patio guide shows the whole job step by step.

Frequently asked questions

How many 600 × 600 slabs in a square metre?

About 2.7 with 10mm joints (2.78 without joints). Allow 10% more for cuts.

Full bed or spot bedding?

A full mortar bed under every slab. Spot bedding (five dabs) leaves hollows that collect water and let slabs rock or crack, and most slab makers no longer recommend it.

Which way should a patio fall?

Away from the house, at about 1:60 to 1:80 (roughly 15mm per metre), so rain runs off rather than sitting on the slabs or against the wall.

Related calculators

Patio & Paving Slab CalculatorSlabs, MOT sub-base, sharp sand, cement and jointing compound. MOT Type 1 Sub-Base CalculatorTonnes and bulk bags of sub-base for patios, paths and driveways. How to Lay a Patio, Step by StepSetting out, dig depth, sub-base, a full mortar bed, porcelain priming, jointing and a patio planner with hand-checked UK prices. How much MOT Type 1 for a patio?