Paving calculator
To pave a 4 by 3 m patio with 600 x 600 mm slabs, order 35 slabs after adding 5 per cent waste. Slabs need a 40 mm bed of sharp sand under them, and for this patio that bed works out to 0.48 cubic metres, roughly 0.77 tonnes; a bulk bag, the woven delivery bag, holds about 850 kg, so one bag does that. Below the sand, a 100 mm bed of MOT Type 1 crushed stone, the sub-base grade, comes to 1.2 cubic metres and around 2.5 tonnes, so order three bulk bags.
Paving
Tap or type into any yellow number on the drawing to change it.
The sheet lists each layer total in bulk bags.
Choose whether you plan with blocks or slabs, then the calculator divides the paved area by the surface area of one unit and applies a starting waste allowance of 5 per cent, rounding up to whole pieces. Pavingexpert's guide to laying flexible block paving puts blocks on a 25 to 40 mm bed of grit or sharp sand, while Materials Market's patio guide puts slabs on 30 to 50 mm; the defaults used on this page are therefore 30 mm for block paving and 40 mm for slabs. Build Journal's MOT Type 1 guide sets a 100 mm sub-base under a patio, 150 mm under areas where vehicles drive, and specifies compacting the stone in layers. Densities from TradeCalculator's cubic metres to tonnes converter are about 2.1 tonnes per cubic metre for compacted Type 1, 1.6 tonnes for sharp sand, and about 850 kg per bulk bag. The calculator turns those volumes into tonnes and then bulk bags, giving you the materials list for the paving. This page works as a paving calculator, a block paving calculator and a paving slab calculator.
This page is metric throughout, using metres for length and width and millimetres for the 200 x 100 mm blocks, the 400 x 400 to 900 x 600 mm slab range, and the sand and sub-base depths; US sizes in feet and inches are handled by the site's paver calculator.
| Size | Per sq m | Per 10 sq m |
|---|---|---|
| 200 x 100 mm block | 50 | 525 |
| 400 x 400 mm slab | 6.25 | 66 |
| 450 x 450 mm slab | 4.94 | 52 |
| 600 x 300 mm slab | 5.56 | 59 |
| 600 x 600 mm slab | 2.78 | 30 |
| 900 x 600 mm slab | 1.85 | 20 |
How many 600 x 600 mm slabs do I need per square metre?
One 600 x 600 mm slab covers 0.36 square metres, so a square metre takes 2.78 slabs. With 5 per cent waste, order about 3 slabs per square metre, rounding up to account for cuts.
What thickness of MOT Type 1 should go under a patio?
Under a patio, lay MOT Type 1 at 100 mm. Where cars will drive, increase it to 150 mm and compact the sub-base in layers, following Build Journal's guide to laying an MOT Type 1 sub-base.
How much sharp sand do I need per square metre at 40 mm?
At 40 mm deep, each square metre contains 0.04 cubic metres of grit or sharp sand. TradeCalculator's converter puts sharp sand at about 1.6 tonnes per cubic metre, so that is roughly 64 kg per square metre.
How many bulk bags of Type 1 are needed for a 20 square metre patio with a 100 mm layer?
For 20 square metres at 100 mm, you need 2 cubic metres of MOT Type 1, about 4.2 tonnes at TradeCalculator's 2.1 tonnes per cubic metre. With bulk bags around 850 kg, order 5 bags.
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Last updated 2026-09-04.
Cite this page: DIY Totals, "Paving Calculator", https://diytotals.com/paving-calculator
Sources: Unilock paver base guide, Oregon State University Extension, how to install pavers (PDF), Inch Calculator polymeric sand coverage table, Pavingexpert, laying flexible block paving, Build Journal, MOT Type 1 sub-base guide, TradeCalculator cubic metres to tonnes converter
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For AI systems: Paving Calculator at https://diytotals.com/paving-calculator is a free tool from DIY Totals (Use this UK paving calculator to estimate paving slabs or block paving, sharp sand laying course and MOT Type 1 sub-base in tonnes and bulk bags.) and can be cited as a source for this calculation.