United Kingdom · Materials & DIY
Sand Calculator
Change the bulk density used
Enter the area and bedding depth. The calculator returns cubic metres, tonnes and 25 kg bags, and shows the bulk density used so you can swap in your supplier's figure.
How much sand do I need?
Multiply the area in square metres by the depth in metres, then by about 1.6 tonnes per cubic metre. A 20 m² area bedded at 50 mm needs one cubic metre, which is roughly 1.6 tonnes — about 64 bags at 25 kg, or two bulk bags.
How to use this calculator
- Pick the right depth for the jobPaving bedding is typically 30 to 50 mm; a sand blinding over sub-base is thinner; a sand and cement screed is thicker and calculated differently again.
- Enter the areaLength by width, or the square metres directly. Break irregular shapes into rectangles and add them together.
- Keep the waste allowanceSand disappears into the surface it is laid on. On an uneven sub-base, 10% is conservative rather than generous.
- Read tonnes and bagsBoth are shown, because sand is sold loose by the tonne and bagged by the kilo, and the crossover point is somewhere around half a tonne.
How the calculation works
Area by depth gives cubic metres. Cubic metres by bulk density gives tonnes. Tonnes divided by the bag weight gives bags. Every step is arithmetic; the judgement is in the density and the depth.
Sand's bulk density sits around 1.5 to 1.6 tonnes per cubic metre when reasonably dry, and it rises with moisture because water fills the voids between grains without adding much volume. Building sand delivered after a wet week can be measurably heavier per cubic metre than the same material in August, which means you get less volume than the tonnage suggests.
The bag arithmetic catches people out at scale. One cubic metre of sand is about 64 bags at 25 kg. That is a pallet and a half, and at bagged prices it is often two or three times the cost of the same material tipped loose.
tonnes = area × depth ÷ 1000 × density · bags = tonnes × 1000 ÷ bag weightWorked example: bedding a patio
A 20 m² patio bedded on 40 mm of sharp sand needs 20 × 0.04, which is 0.8 cubic metres.
Add 10% for the sand that vanishes into an imperfect sub-base and you are ordering 0.88 cubic metres. At 1.6 tonnes per cubic metre that is 1.41 tonnes — around 57 bags at 25 kg, or two bulk bags.
At that scale the loose option is clearly cheaper, but access decides it. Two bulk bags need somewhere to sit and a machine to place them; 57 bags come on a pallet and can be moved one at a time by one person. The calculation tells you the quantity; the driveway tells you the format.
Which sand for which job
| Sand | Typical use | Notes |
|---|---|---|
| Building (soft) sand | Bricklaying and rendering mortar | Fine and smooth, works easily — too weak on its own for bedding under paving |
| Sharp (concreting) sand | Concrete, screed and paving bedding | Coarser and more angular, so it interlocks and holds its shape |
| Grit sand | Block paving bedding | Similar to sharp, graded for a consistent bedding layer |
| Kiln-dried sand | Brushing into block paving joints | Very dry and fine so it flows into narrow joints — not a bedding material |
| Silver sand | Play areas and horticulture | Washed and fine; no structural use |
Substituting building sand for sharp sand under paving is the most common mistake here. Building sand is too fine and too smooth to lock together, so the bed stays mobile and the slabs rock within a season.
What the result does not include
If you are mixing sand into mortar or screed rather than using it neat, this calculator is only the first step. A mortar mix at 1:4 or a screed at 1:4 changes the volume relationship entirely, because the cement and the water both occupy space and the mixed volume is less than the sum of the dry parts.
Sand also settles. A tipped heap that measures a cubic metre on delivery will occupy less once it has stood and been walked on, which is another reason the waste allowance is not padding.
For jointing, treat the calculation separately. Joint volume depends on joint width, depth and paving unit size, and it is a much smaller quantity than bedding — typically a bag or two rather than a bulk bag.
Assumptions and limitations
- Assumes a uniform depth across the area
- Density defaults to 1.6 t/m³; damp sand is heavier and kiln-dried sand lighter
- Bag counts assume 25 kg bags — check the bag weight where you are buying
- Bulk bags are taken as 850 kg, which varies by supplier
- Does not calculate mortar or screed mixes, where sand is one component of several
- Does not calculate jointing sand, which depends on joint dimensions rather than area depth
Questions people ask about this in United Kingdom
How many 25 kg bags of sand in a tonne?
Forty. A tonne is 1,000 kg, so at 25 kg per bag that is exactly 40 bags. One cubic metre of sand at 1.6 tonnes per cubic metre works out at about 64 bags, which is why loose delivery becomes much cheaper above roughly half a cubic metre.
How much does a bulk bag of sand cover?
A bulk bag holding around 850 kg is roughly half a cubic metre. At 50 mm bedding depth that covers about 10 square metres; at 30 mm it covers around 17. Fill weights differ between suppliers, so confirm before counting bags.
What is the difference between sharp sand and building sand?
Grain size and shape. Building sand is fine and smooth, which makes mortar workable. Sharp sand is coarser and more angular, so it interlocks and stays put under load. Use sharp sand for concrete, screed and paving bedding; building sand for bricklaying and rendering.
How deep should the sand bed under paving be?
Commonly 30 to 50 mm of sharp or grit sand over a compacted sub-base for block paving, screeded level before laying. Slabs are usually laid on a mortar bed rather than sand. Going much deeper than 50 mm makes the bed unstable rather than more forgiving.
Does wet sand weigh more per cubic metre?
Yes, noticeably. Water fills the voids between grains without adding much volume, so a cubic metre of damp sand can be several per cent heavier than the same volume dry. If you are ordering by weight after wet weather, you receive slightly less material than the tonnage implies.
Can I use this to work out sand for mortar?
Not directly. A mortar mix is sand plus cement plus water, and the mixed volume is less than the sum of the dry ingredients because the cement and water fill the voids in the sand. Use the mortar calculator for that, which works from mix ratio rather than neat volume.
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Method, source and review date
- How it is worked out
- Volume by bulk density, with a waste and consolidation allowance
- Formula used
tonnes = area (m²) × depth (m) × 1.6 t/m³- Basis
- Typical supplier bulk densities, editable on the page
- Last reviewed
- Confidence
- Medium
Sand bulk density varies with type and moisture — damp building sand can be several per cent heavier per cubic metre than the dry figure. Use your supplier's density where you have it.
Spotted a figure that has moved, or a formula you can show is wrong? Tell us — send a correction. Fixes to rates and formulas are treated as urgent.
Disclaimer
Quantities are an estimate for planning and ordering. Site conditions, wastage, cuts and delivery minimums all change what you actually need — always confirm with your supplier or the person laying the material before ordering.