How Many Paving Slabs Do I Need? Slabs per m², Sub-base and Sand (UK)
A 4 × 3 m patio (12 m²) needs 36 paving slabs of 600 × 600 mm, including 10% for cutting and 10 mm joints. Under them goes 2.8 tonnes of MOT Type 1 (100 mm) and 0.6 tonnes of sharp sand (30 mm). The paving calculator works it out for your own area, slab size and joints.
Slabs per square metre
With a 10 mm joint and with no allowance for joints, and no cutting waste:
| Slab size | Slabs per m² (10 mm joint) | Slabs per m² (no joint) |
|---|---|---|
| 600 × 600 mm | 2.69 | 2.78 |
| 450 × 450 mm | 4.73 | 4.94 |
| 400 × 400 mm | 5.95 | 6.25 |
| 300 × 300 mm | 10.41 | 11.12 |
| 600 × 300 mm | 5.29 | 5.56 |
| 900 × 600 mm | 1.81 | 1.86 |
Slabs, sub-base and sand by area
For 600 × 600 mm slabs and 450 × 450 mm slabs, with 10 mm joints and 10% waste. The MOT Type 1 is 100 mm deep and the sand 30 mm, for the 600 mm slabs:
| Area | 600 × 600 mm slabs | 450 × 450 mm slabs | MOT Type 1 | Sharp sand |
|---|---|---|---|---|
| 5 m² | 15 | 26 | 1.16 t | 0.25 t |
| 10 m² | 30 | 52 | 2.31 t | 0.50 t |
| 15 m² | 45 | 78 | 3.47 t | 0.76 t |
| 20 m² | 60 | 104 | 4.62 t | 1.01 t |
| 30 m² | 89 | 156 | 6.93 t | 1.51 t |
| 40 m² | 119 | 208 | 9.24 t | 2.02 t |
How to lay slabs
- Dig out to the depth of the sub-base, the bed and the slab: about 100 mm of MOT Type 1, 30 mm of bedding and the slab thickness, with a fall of about 1 in 80 away from buildings.
- Lay and compact the MOT Type 1 in layers with a plate compactor.
- Spread the bedding. A layer of sharp sand about 30 mm thick suits a patio, and a full mortar bed (six parts sand to one of cement) suits slabs that carry vehicles. A mortar bed takes 6 bags of cement here.
- Lay each slab and tap it down with a rubber mallet, checking the level and the fall as you go.
- Joint the slabs with a jointing compound or a dry sand and cement mix, once they are set.
Choosing slabs and planning the layout
- Large slabs (600 × 600 mm and bigger) need fewer joints but are heavy to lift and need a firm bed. Smaller slabs are easier to handle and to cut round curves.
- Plan the layout so that you cut as few slabs as you can, and put the cut slabs at the edges where they are least visible.
- Add 10% for cuts and breakage, and more for a diagonal layout or a pattern with several sizes.
- Buy all the slabs at one time: colours differ between batches. Mix slabs from several packs as you lay them.
- In England, paving a front garden of more than 5 m² with an impermeable surface needs drainage or permeable materials, or planning permission.
For the bedding concrete, see the concrete calculator, and for stone the gravel calculator. These quantities are estimates: confirm them with your supplier.
Frequently asked questions
How many 600 × 600 paving slabs do I need per m²?
About 2.69 slabs per m² with 10 mm joints, which is 2.78 slabs if there is no gap. Add 10% for cuts.
How many slabs for a 4 × 3 m patio?
36 slabs of 600 × 600 mm for 12 m², with 10% for cutting and 10 mm joints.
How much MOT Type 1 do I need for a patio?
A 100 mm sub-base for a 12 m² patio takes about 2.8 tonnes. A 150 mm sub-base for a drive takes 4.2 tonnes.
How much sharp sand for laying slabs?
A 30 mm bed for a 12 m² patio takes about 0.6 tonnes of sharp sand. A full mortar bed uses 6 bags of cement for the 12 m² of the default job.
What fall should a patio have?
A slope of about 1 in 80 (12 mm per metre) away from the house, so that water drains off and does not pool.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.