Calculate sharp sand for laying patios, bedding slabs, screeding and rendering. Enter the area and depth and get litres, cubic metres and the best-value bags.
A sharp sand bed under slabs is usually 5cm deep over a compacted sub-base. One bulk bag covers about 14m² at that depth.
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5 cm
Depth changes the volume a lot — 5cm mulch is normal, raised veg beds want 20cm+.
Not sure? See the depth guide belowSharp sand for bedding slabs, screeds and drainage — by area and depth.
Worked example: patio bedding layer
A 12m² patio on a 5cm sand bed needs 12 × 5 × 10 = 600 litres of sharp sand — comfortably one bulk bag. Add cement separately if you're laying on a full mortar bed.
Match the sand to the job, because they're not interchangeable: sharp (grit) sand has coarse angular grains for bedding paving, screeds and renders; building (soft) sand makes workable bricklaying mortar; kiln-dried sand is brushed into block-paving joints after laying. For bedding, 30–50mm of compacted sharp sand over a solid sub-base is the norm — a sand-only bed under slabs shifts and the slabs rock, so patios want a full 4:1 sharp-sand-and-cement mortar bed instead.
Sand weighs roughly 1.6 tonnes per cubic metre, and a standard 850L bulk bag covers about 17m² at 50mm deep. Watch for bulking: damp sand swells by up to a quarter in volume, so if you're gauging mortar by the shovel, a heap of wet sand contains less actual sand than it looks. Order 5–10% extra for screed levelling and settlement, and keep handy bags for small pointing top-ups where a bulk bag would be overkill.
Sharp (grit) sand is coarse and drains freely — use it under slabs and in concrete. Building (soft) sand is finer and used for mortar and pointing.
Last reviewed: October 2026 · Reviewed by the Garden Calculator editorial team.
Garden Calculator — Project
My garden project · 28 October 2026
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