UK Gravel Calculator
Ordering gravel goes wrong in one of two ways: you order by area and forget depth, or you order in bulk bags without checking what a bulk bag actually weighs at your supplier. This calculator takes your area, your depth and the type of gravel you are laying, then gives you the volume in cubic metres, the weight in tonnes, and the number of bags to order. It uses UK gravel densities and UK bag sizes throughout.
Enter a number greater than zero.
Enter a number greater than zero.
Enter your dimensions and depth above to see your gravel estimate.
How much gravel do you need per square metre?
At the 50mm depth used for most UK driveways, one square metre takes roughly 0.05 m³ of gravel, which is about 80 kg at a typical density of 1.6 tonnes per cubic metre. A standard 850 kg bulk bag therefore covers somewhere around 10 to 11 square metres at that depth.
That figure shifts with depth and with the stone itself. Slate chippings are noticeably lighter than gravel, so the same volume weighs less and you need fewer bags by weight. Granite and limestone sit between the two.
Takeaway: as a rough sanity check before you order, one 850 kg bulk bag covers about 10 m² at 50mm depth.
The formula
The calculation is volume first, weight second:
- Area in square metres. Length times width for a rectangle, or π times radius squared for a circle.
- Volume in cubic metres. Area times depth, with depth converted to metres (50mm becomes 0.05).
- Add wastage. Multiply by 1.05 for 5%, which covers settling, spillage and uneven ground.
- Convert to weight. Multiply volume by the density of the stone in tonnes per cubic metre.
- Convert to bags. Divide the weight in kilograms by your bag size, then round up.
Rounding up matters at step five. Suppliers do not sell part bags, and running 40 kg short means either a second delivery charge or a visible join where the new stone meets the old.
Takeaway: always round bag counts up, never to the nearest whole bag.
What depth do you actually need?
| Application | Gravel depth | Sub-base required |
|---|---|---|
| Decorative borders and beds | 30–40 mm | Membrane only |
| Footpaths, light foot traffic | 40–50 mm | 50–100 mm compacted |
| Gravel driveway, surface layer | 50 mm | 100–150 mm MOT Type 1, compacted |
| Driveway sub-base | 100–150 mm | Compacted subgrade |
The sub-base does the structural work. Aggregates for this use are covered by BS EN 13242, and MOT Type 1 to the Specification for Highway Works Series 800 is the standard choice under a UK driveway. The gravel you can see is a wearing surface, not a load-bearing layer.
Takeaway: budget for a sub-base separately. It is usually the larger of the two aggregate orders.
Why deeper is not better
Most guidance tells you to go deeper for a driveway. On the surface layer, the opposite is true. Gravel laid much beyond 50mm behaves like loose ballast: tyres cut ruts into it, it drifts towards the edges, and walking on it feels like walking on sand. Deep gravel also finds its way onto the pavement every time a car pulls off the drive.
If a driveway feels soft, the fix is nearly always a thicker compacted sub-base underneath, not more stone on top. In practice most UK groundworkers lay 100 to 150mm of MOT Type 1, whack it down properly, then finish with a single 50mm layer of 20mm gravel. Angular stone such as granite or limestone locks together better than rounded pea shingle, which is why pea shingle tends to migrate on a drive even at the correct depth.
Takeaway: if you are tempted to order more gravel to fix a soft driveway, order sub-base instead.
Gravel types and densities
| Gravel type | Typical size | Density (t/m³) | Best for |
|---|---|---|---|
| 20mm gravel / shingle | 20 mm | 1.60 | Driveways, paths |
| 10mm pea shingle | 10 mm | 1.60 | Borders, beds |
| Slate chippings | 20–40 mm | 1.30 | Decorative beds |
| Granite chippings | 14–20 mm | 1.50 | Driveways, paths |
| Limestone chippings | 20 mm | 1.50 | Paths, drives |
| Cotswold / buff chippings | 20 mm | 1.50 | Decorative areas |
| MOT Type 1 (compacted) | 0–40 mm | 2.00 | Sub-base |
Densities are for dry, loose material. Wet stone weighs more, so a bulk bag delivered after a week of rain can be noticeably heavier than the labelled weight suggests.
Takeaway: check the density of your specific stone if you are buying decorative chippings, because slate can throw a weight-based order out by 20%.
Worked example
A gravel driveway in Preston, 9 m long by 3.5 m wide, finished in 20mm golden gravel at 50mm depth with 5% wastage.
- Area: 9 × 3.5 = 31.5 m²
- Volume before wastage: 31.5 × 0.05 = 1.575 m³
- Volume with 5% wastage: 1.575 × 1.05 = 1.654 m³
- Weight: 1.654 × 1.6 = 2.65 tonnes (2,646 kg)
- Bulk bags at 850 kg: 2,646 ÷ 850 = 3.11, rounded up to 4 bags
- 25 kg bags: 2,646 ÷ 25 = 105.8, rounded up to 106 bags
Four bulk bags against 106 small bags is the whole argument for bulk delivery on anything driveway-sized. The same driveway also needs roughly 3.5 to 5.3 m³ of MOT Type 1 underneath at 100 to 150mm, which is a separate and considerably heavier order at 2.0 t/m³.
Takeaway: for anything over about 15 m², price bulk bags rather than 25 kg bags before you order.
Bulk bags, loose tipped, or small bags
A "bulk bag" is not a standard unit. Depending on the merchant it might be 800 kg, 850 kg, or sold as a "tonne bag" that contains somewhere near 1,000 kg. Travis Perkins, Jewson and Wickes all list their own weights, and the difference between 800 and 1,000 kg across four bags is a whole extra bag of stone.
Loose tipped delivery, where the lorry tips straight onto the drive, is usually the cheapest option per tonne once you are ordering above roughly five tonnes. It needs somewhere to tip and someone to move it. Small 25 kg bags from B&Q or Wickes make sense for borders and small repairs and almost nowhere else.
As a rough 2026 guide, a bulk bag of 20mm gravel delivered typically runs somewhere around £65 to £95 depending on region and stone, decorative slate sits higher at roughly £90 to £130, and loose tipped bulk loads come down towards £45 to £65 per tonne. Delivery charges and regional variation move these figures a long way, so treat them as a starting point rather than a quote.
Takeaway: confirm the bag weight in kilograms before comparing prices between merchants.
Planning and drainage
Gravel is a permeable surface. Under the 2008 planning rules covering front gardens in England, a new driveway over five square metres needs planning permission if it uses an impermeable surface without drainage to a permeable area. Loose gravel over a permeable build-up generally sidesteps that, which is a genuine practical advantage over block paving or tarmac.
Takeaway: gravel is one of the simpler driveway surfaces to install without a planning application, but check with your local authority before assuming.
Frequently asked questions
Related tools
- UK Topsoil Calculator — volume, litres, tonnes and bulk bags for topsoil
- Driveway Cost Calculator — estimate block paving, resin, gravel or tarmac costs
- Gravel Under Concrete Slab Calculator — sub-base volume and bulk bags beneath a concrete slab
- Landscape Services Estimate Template — build a full itemised landscaping quote
Guides worth reading
- How Much Gravel Do I Need? UK Guide — worked examples, depth rules, densities and 2026 prices
- How Much Does a Driveway Cost in the UK? — full cost breakdown by material
Disclaimer: This calculator gives estimated quantities for planning and budgeting. It is not a substitute for advice from a qualified groundworker, structural engineer or building control officer. Ground conditions, drainage, access and local authority requirements vary. Always confirm quantities and build-up with your supplier and contractor before ordering.