Paving block calculator

This calculator tells you how many paving blocks, bricks, or slabs you need to cover a given area. Enter the dimensions of the area you are paving and the size of a single block, add a waste allowance, and it returns the total number of blocks required — plus how many fit per square metre.

How it works

The tool divides the total area by the area of one block to find how many are needed, then adds your waste percentage to cover cuts, breakages, and the off-cuts you cannot reuse. A 5–10% allowance is sensible for a simple layout, and 10–15% for diagonal or herringbone patterns where there are more cuts.

Don’t forget the base layers

Paving needs a solid foundation: a compacted MOT Type 1 sub-base topped with laying sand. Work out the sub-base with our MOT Type 1 calculator and the overall area with the construction area calculator.

Frequently asked questions

How many 20 × 10 cm blocks per square metre?

Fifty blocks per square metre, since each covers 0.02 m². The calculator adjusts automatically for any block size you enter.

Disclaimer: Estimates only. Order a little extra and keep some spares for future repairs.

How many paving blocks per square metre?

The number of units per square metre depends only on the face size of each block or slab. Divide 1 m² (10,000 cm²) by the area of one unit in cm². The table below covers the sizes most often sold by UK builders’ merchants, with the figure rounded to two decimal places before any waste allowance.

Unit size (mm)	Typical use	Units per m²
200 × 100	Block paving for driveways	50.00
215 × 102.5	Clay pavers	45.38
400 × 400	Concrete patio slabs	6.25
450 × 450	Utility slabs	4.94
600 × 300	Porcelain and sandstone plank	5.56
600 × 600	Sandstone and porcelain patios	2.78
900 × 600	Large-format paving	1.85

Worked example: block paved driveway

A driveway measuring 6 m by 4 m has an area of 24 m². Using standard 200 × 100 mm blocks at 50 per m², you need 1,200 blocks before waste. A herringbone pattern creates lots of cut pieces along the edges, so add 10%: 1,200 × 1.10 = 1,320 blocks. Block paving is usually sold in packs covering roughly 8–10 m², so this drive needs about three packs — always check the exact pack coverage with your supplier.

The same drive has a perimeter of 2 × (6 + 4) = 20 m. If every edge needs a restraint, that is 20 m of kerb or edging — about 100 edging units at 200 mm long — less any length running against a wall or house.

Worked example: slab patio

A 4 m by 3 m patio covers 12 m². Each 600 × 600 mm slab covers 0.36 m², so 12 ÷ 0.36 = 33.3, which rounds up to 34 slabs. A straight-laid patio needs only a small waste allowance, so 5% gives 35 slabs. Joints of around 10 mm slightly reduce the number you actually lay, so the calculator’s figure is on the safe side.

Sub-base and bedding quantities

The blocks are only the visible layer. Driveways that carry cars normally need about 150 mm of compacted MOT Type 1 sub-base, while a footpath or patio usually needs 100 mm. For the 24 m² driveway above, 24 × 0.15 = 3.6 m³ of Type 1, which at roughly 2.1 tonnes per m³ compacted is around 7.6 tonnes. Use the MOT Type 1 calculator to refine this figure.

Block paving then sits on a 30–50 mm bed of grit or sharp sand. At 40 mm, the driveway needs 24 × 0.04 = 0.96 m³ — roughly 1.5 tonnes of sand. Slabs are normally bedded on a 25–40 mm mortar mix instead of loose sand.

Imperial sizes for US pavers

If you work in feet, convert first: 1 m² equals 10.764 ft². A common US paver measuring 4 × 8 inches covers 0.222 ft², so you need 4.5 pavers per square foot. A 12 × 20 ft patio (240 ft²) therefore needs 1,080 pavers before waste, or about 1,134 with a 5% allowance. The area converter handles any other unit change.