How this calculator works
This runs our paving calculator on your measurements. Each slab covers its own size plus a joint, so the number of slabs is the area plus waste divided by that. Under the slabs go a compacted sub-base of MOT Type 1 and a bed of sharp sand, or a full mortar bed for heavier use.
Worked example: a 4 × 3 m patio (12 m²) in 600 × 600 mm slabs with 10 mm joints and 10% for cuts needs 36 slabs, 2.8 tonnes of MOT Type 1 for a 100 mm sub-base and 0.6 tonnes of sharp sand for a 30 mm bed. With a mortar bed instead it is 0.9 tonnes of sand and 6 bags of cement.
Patio materials by size (600 × 600 mm slabs, 100 mm sub-base, sand bed)
10 mm joints and 10% for cuts.
| Patio | Slabs | MOT Type 1 | Sharp sand | Edging |
|---|---|---|---|---|
| 3 × 3 m | 27 | 2.1 tonnes | 0.5 tonnes | 12 m |
| 4 × 3 m | 36 | 2.8 tonnes | 0.6 tonnes | 14 m |
| 4 × 4 m | 48 | 3.7 tonnes | 0.8 tonnes | 16 m |
| 5 × 4 m | 60 | 4.6 tonnes | 1.0 tonnes | 18 m |
| 6 × 5 m | 89 | 6.9 tonnes | 1.5 tonnes | 22 m |
Tips before you buy
- Compact the MOT Type 1 in layers of about 100 mm with a plate compactor. A poor sub-base is the main reason a patio sinks.
- Use a full mortar bed on a drive or anywhere a vehicle will go, and for natural stone. A sharp sand bed is fine for a garden patio.
- Order the slabs from one batch, and a couple extra for later repairs. Colours and sizes vary between runs.
- Check for buried services before you dig, using the free LSBUD service.
- Fill the joints with a dry mortar mix, resin or a brush-in jointing compound, as the slab maker recommends.
Tools & materials for this project
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Frequently asked questions
How many paving slabs do I need for a 4m x 3m patio?
36 slabs of 600 × 600 mm with 10 mm joints and 10% for cuts. Without any allowance for cuts it is 33.
How much MOT Type 1 do I need for a patio?
About 0.22 tonnes per m² for a 100 mm compacted layer, so a 12 m² patio needs 2.8 tonnes with 5% extra. That is 4 bulk bags of 0.8 tonnes.
Should I lay slabs on sand or mortar?
A sharp sand bed is fine for a garden patio, and quicker to adjust. Use a full mortar bed on a drive or anywhere a vehicle will go, and for natural stone.
How deep should the sub-base be for a patio?
A compacted layer of 100 mm of MOT Type 1 suits most patios and paths. For a driveway use 150 mm or more, and on soft clay ground go deeper.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.