Calculate how many patio paving slabs you need, plus sub-base and bedding, for standard UK slab sizes.
This paving slab calculator works out how many patio slabs you need for a given area, plus the MOT Type 1 sub-base and bedding underneath. It's for anyone laying a patio, path or terrace who wants an accurate slab count — including standard UK slab sizes — before ordering.
For a patio 5 m × 4 m using 600 × 600 mm slabs with a 10 mm joint:
For 600 × 600 mm slabs you need about 2.8 per m², for 450 × 450 mm about 4.9 per m², and for 600 × 300 mm about 5.6 per m². This calculator works it out exactly from your area, chosen slab size and joint width.
Allow around 5% for a simple square or rectangular patio and up to 10% for patios with lots of cuts, curves or diagonal laying patterns.
A compacted MOT Type 1 sub-base (typically 100 mm) topped with a bedding layer of mortar or sharp sand (around 30-50 mm). This calculator estimates both for you.
For a patio, a full wet mortar bed is best as it gives firm, even support. Sand or a screeded bed is usually only suitable for lighter-duty paths and pedestrian areas.
Aim for a gentle fall of about 1:80 (roughly 12 mm per metre) directed away from the house so rainwater runs off rather than pooling.
