How many paving slabs do I need?
Last reviewed 1 July 2026
Short answer
Divide the patio area by the module area — the slab size plus one joint width in each direction — then add a waste allowance for cuts. A 20 m² patio in 600 × 600 mm slabs with 10 mm joints needs 20 ÷ (0.61 × 0.61) = 53.8, so 54 slabs before waste, and 60 with a 10% allowance.
Work it out for your project with the patio and paving calculator →
Use the module, not the slab
A 600 × 600 mm slab does not cover 0.36 m² of patio. With a 10 mm joint it occupies a 610 × 610 mm module, which is 0.3721 m². That is 3.3% more coverage per slab than the raw slab area suggests.
On a 20 m² patio the difference is two slabs. On block paving with small units and thin joints it is proportionally larger, because the joint is a bigger fraction of a 200 × 100 mm unit than of a 600 mm slab.
Ignoring the joint over-orders. That is a less dangerous error than under-ordering, but it is still money on the driveway you did not need to spend.
slabs = area ÷ ((slab length + joint) × (slab width + joint))
Slabs per square metre
| Slab size | Joint | Module | Per m² | Per 10 m² |
|---|---|---|---|---|
| 600 × 600 mm | 10 mm | 610 × 610 | 2.69 | 27 |
| 450 × 450 mm | 10 mm | 460 × 460 | 4.73 | 48 |
| 600 × 300 mm | 5 mm | 605 × 305 | 5.42 | 55 |
| 200 × 100 mm block | 3 mm | 203 × 103 | 47.8 | 478 |
| 16 × 16 in paver | ⅜ in | 16.375 × 16.375 | 0.537 per ft² | — |
| 8 × 4 in paver | ⅛ in | 8.125 × 4.125 | 4.30 per ft² | — |
Then add for the pattern
A straight grid on a rectangular patio wastes very little — you cut one row down one edge if the dimensions do not divide evenly.
A running bond needs a half unit at alternate ends of every row, which produces waste unless you can pair the offcuts.
Herringbone is the expensive one. Every perimeter unit is a diagonal cut and the offcuts rarely pair up. Fifteen per cent is a floor, not a comfortable allowance.
| Pattern | Allowance | Why |
|---|---|---|
| Straight grid (stack bond) | 5% | Cuts only along two edges |
| Running bond (stretcher) | 7% | Half units at alternate row ends |
| Basket weave | 10% | Needs a strict 2:1 unit ratio; edges rarely work out |
| Herringbone 45° | 15% | Every perimeter unit is a diagonal cut |
| Random-size pack | 10% | Coverage varies and layout cannot be planned exactly |
Random-size packs
Mixed-size packs — common for riven sandstone and some porcelain ranges — cannot be counted by unit size, because the mix of sizes varies between suppliers and sometimes between batches.
Use the coverage printed on the pack. If a pack covers 10 m² and you have 30 m² of patio, you need three packs plus a waste allowance, so four.
Set several square metres out dry before you bed anything down, and order all the packs at once from the same batch so the colours match.
Important: Order it all in one go
Check the weight before you check the price
A 600 × 600 × 35 mm concrete slab weighs about 28 kg. Anything over 25 kg is a two-person lift, and large-format 900 × 600 slabs at 20 mm porcelain or 40 mm stone are heavier still.
Paving is delivered on pallets of around a tonne. Work out how many pallets you need, and make sure there is somewhere firm and level for them within reach of the lorry's crane.
Related questions
- How many 600 × 600 slabs are in a square metre?
- 2.69 with a 10 mm joint, or 2.78 if you ignore the joint. Over ten square metres that is 27 slabs rather than 28.
- Should I order spare slabs?
- Yes. Keep two or three spares from the same batch after the job is finished. Replacing a cracked slab in five years from a current batch will not match.
Safety notice: Material planning only