Overview
The bedding course sits between sub-base and blocks — it is screeded, not compacted loose, so measure the finished thickness.
How the calculation works
Sharp sand weight = area × screeded thickness × 1.6 t/m³, so each 25mm per 10 m² adds 0.4 tonnes.
The same tonnage feeds concrete work: sharp sand is half of a standard 1:2:4-style blend with cement and gravel.
Bulk bags are filled by weight, so a nominally 'tonne' bag at 850kg covers about 10.6 m² at 50mm.
Worked example
A slabbed patio 25 m² uses a 30mm sharp sand bed under slabs on a full sub-base.
Volume = 25 × 0.03 = 0.75 m³. Weight = 0.75 × 1.6 = 1.2 tonnes.
A 10% allowance takes the order to 1.32 tonnes — two 850kg bulk bags with spare for jointing.
Sharp sand at a glance
- Planning density1.60 t/m³
- Typical range1.50–1.70 t/m³
- CategorySand
- CompactionUsually not applied
- SourcePlanning value based on typical UK sharp sand bulk densities
- Reviewed2026-08-16
Planning values for typical UK supplies; your supplier product data takes precedence.
Sharp sand coverage guide
| Depth | Area per tonne | Area per 850kg bag | Weight per m² |
|---|---|---|---|
| 25mm | 25.0 m² | 21.3 m² | 40 kg |
| 40mm | 15.6 m² | 13.3 m² | 64 kg |
| 50mm | 12.5 m² | 10.6 m² | 80 kg |
| 75mm | 8.3 m² | 7.1 m² | 120 kg |
| 100mm | 6.3 m² | 5.3 m² | 160 kg |
| 150mm | 4.2 m² | 3.5 m² | 240 kg |
Computed from a 1.60 t/m³ planning density on level ground.
Assumptions and accuracy
1.6 t/m³ is a planning value for dry-ish coarse grit sand; wet deliveries run heavier.
Screed and concrete quantities also depend on the cement and aggregate components calculated separately.
Confirm final quantities with your supplier, especially for screeds with strict level tolerances.
How to use this calculator
- Measure the area to be bedded.
- Enter the screeded sand thickness (30-50mm is typical under slabs and blocks).
- Keep sharp sand selected — its coarse grading is what locks paving down.
- Add a small allowance for edge losses and levelling.
When sharp sand is commonly used
Sharp sand beds block paving and natural stone slabs, forms floor screeds with cement, backfills trenches above pipe bedding, and provides grit for snow topping and play pits.
Frequently asked questions
How much sharp sand do I need for paving?
For a 50mm bedding course allow 80kg per square metre; at 30mm allow about 48kg. Multiply by your area and add 5-10%.
How many bulk bags of sharp sand for 20 m²?
At 50mm deep, 20 m² needs about 1.6 tonnes plus allowance — two 850kg bulk bags.
Is grit sand the same as sharp sand?
Yes — 'grit sand', 'sharp sand' and 'coarse sand' all describe the angular washed sand used for bedding and concrete. Building (soft) sand is a different material.
Does sharp sand need compacting?
A bedding course is screeded level and lightly compacted before laying — over-compacting displaces it and loses the level. Compact the sub-base below thoroughly instead; that layer carries the load.
References and source notes
- Typical UK sharp sand bulk density from supplier technical data (planning value).