How Much Gravel Do I Need? A UK Guide
Published 24 July 2026 · Browse all tools
Gravel is one of the few materials where getting the order wrong is obvious the moment the lorry leaves. Too little and you have a visible join. Too much and you are shovelling the surplus into a corner of the garden for the next two years. The maths is not difficult, but two things trip people up: forgetting that depth matters as much as area, and assuming a bulk bag is a fixed weight. This guide covers both, with worked numbers you can check against your own job.
If you want the answer without the reading, the UK Gravel Calculator does the conversion for you.
The short answer
At 50mm depth, one square metre of standard 20mm gravel comes to roughly 0.05 m³, or about 80 kg. A typical 850 kg bulk bag therefore covers somewhere around 10 to 11 square metres.
Scale that up and a small parking area of 30 m² needs about 1.5 m³, or 2.4 tonnes, which is three bulk bags once you round up. A garden path 10 m long and 1 m wide at 40mm depth needs 0.4 m³, roughly 640 kg, which is a single bulk bag with a little left over.
Takeaway: for a quick estimate, multiply your area in square metres by 80 to get the weight in kilograms at 50mm depth.
Working it out properly
The calculation runs in five steps.
Start with area. Length times width for a rectangle. For a circular bed or turning area, π times the radius squared, where the radius is half the diameter.
Convert your depth to metres. 50mm becomes 0.05, 40mm becomes 0.04. This is the step people skip, and it is the reason quantities come out ten or a hundred times wrong.
Multiply area by depth to get volume in cubic metres.
Add wastage. Five per cent is the standard allowance and covers settling, spillage during barrowing, and ground that is not quite as flat as it looked. On a sloping site or where you have dug out by hand, ten per cent is more realistic.
Convert volume to weight by multiplying by the density of your stone. Standard gravel is about 1.6 tonnes per cubic metre. Then divide the weight in kilograms by your bag size and round up.
Takeaway: convert depth to metres before you multiply, and round bag counts up rather than to the nearest whole number.
How deep should it go?
Below about 30mm the membrane or soil beneath starts to show through, particularly on paths where feet scuff the stone aside. Above 50mm on a surface layer you run into the problem in the next section.
The sub-base is a separate order and usually the bigger one. Aggregates for unbound sub-base use fall under BS EN 13242, and MOT Type 1 specified to the Specification for Highway Works Series 800 is the standard choice beneath a UK driveway. At around 2.0 tonnes per cubic metre compacted, it is also considerably heavier per cubic metre than the decorative stone on top.
Takeaway: price the sub-base at the same time as the gravel, because it is typically the larger tonnage of the two.
| Application | Gravel depth | Sub-base |
|---|---|---|
| Decorative borders and beds | 30–40 mm | Membrane only |
| Footpaths | 40–50 mm | 50–100 mm compacted |
| Driveway surface layer | 50 mm | 100–150 mm MOT Type 1 |
| Driveway sub-base | 100–150 mm | Compacted subgrade |
The bit most guides get wrong
Almost every piece of driveway advice tells you that if the surface feels loose, you need more gravel. On the surface layer, more gravel makes it worse.
Gravel much beyond 50mm deep stops behaving like a surface and starts behaving like ballast. Tyres cut ruts into it rather than rolling over it. It drifts towards the edges and out onto the pavement. Walking across it feels unstable, which matters if anyone in the house uses a stick or a pushchair.
A soft driveway is nearly always a sub-base problem. In practice most UK groundworkers excavate to around 200mm, lay and compact 100 to 150mm of MOT Type 1 in layers, then finish with one 50mm layer of 20mm angular stone. The angular shape is doing real work there: granite and limestone chippings lock against each other under load, whereas rounded pea shingle rolls, which is why pea shingle migrates on a drive no matter how carefully it was laid.
Takeaway: if your drive feels soft, order sub-base rather than more surface gravel.
Gravel types and what they weigh
The slate figure is the one worth noting. At 1.3 t/m³ it is around 19% lighter than standard gravel, so ordering slate by weight using a gravel density leaves you well short. Densities also assume dry material. Stone that has sat in a yard through a wet week weighs more per bag than the label suggests, which is in your favour on a weight-priced order and against you on a volume-priced one.
Takeaway: check the density of decorative stone separately, because slate can throw a weight-based order out by nearly a fifth.
| Type | Size | Density (t/m³) | Typical use |
|---|---|---|---|
| 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 |
| 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 |
Worked example one: a driveway in Preston
A gravel driveway 9 m long by 3.5 m wide, finished in 20mm golden gravel at 50mm, with 5% wastage.
- Area: 9 × 3.5 = 31.5 m²
- Volume before wastage: 31.5 × 0.05 = 1.575 m³
- With 5% wastage: 1.575 × 1.05 = 1.654 m³
- Weight: 1.654 × 1.6 = 2.65 tonnes, or 2,646 kg
- Bulk bags at 850 kg: 2,646 ÷ 850 = 3.11 → 4 bags
- 25 kg bags: 2,646 ÷ 25 = 105.8 → 106 bags
The same driveway needs a sub-base underneath. At 125mm of MOT Type 1: 31.5 × 0.125 = 3.94 m³, which at 2.0 t/m³ is roughly 7.9 tonnes. That is three times the weight of the visible gravel and, on most quotes, the larger line item.
Takeaway: on a driveway, expect the sub-base to weigh two to three times what the surface gravel does.
Worked example two: a garden path in Chester
A path 12 m long and 900mm wide, in 10mm pea shingle at 40mm depth, 5% wastage.
- Area: 12 × 0.9 = 10.8 m²
- Volume: 10.8 × 0.04 = 0.432 m³
- With wastage: 0.432 × 1.05 = 0.454 m³
- Weight: 0.454 × 1.6 = 0.73 tonnes, or 726 kg
- Bulk bags at 850 kg: 1 bag, with roughly 124 kg spare
One bag covers it, which is the useful result here. Ordering two would have left most of a bulk bag sitting on the drive. Below about one and a half bags of requirement, it is worth checking whether a smaller area or a slightly reduced depth brings you comfortably under a single bag.
Takeaway: when your requirement lands just over a bag boundary, revisit your depth before ordering the extra bag.
Bulk bags, tonne bags and the weight trap
There is no legal standard for what a bulk bag contains. Merchants variously sell 800 kg bags, 850 kg bags, and "tonne bags" that hold close to 1,000 kg. Travis Perkins, Jewson, Wickes and B&Q each publish their own weights, and the gap matters: four bags at 800 kg is 3.2 tonnes, four at 1,000 kg is 4 tonnes.
That difference also breaks price comparison. A bag at £70 is not cheaper than one at £80 if the first holds 800 kg and the second holds 1,000 kg. Convert everything to a price per tonne before deciding.
Loose tipped delivery, where the lorry tips straight onto the drive or a board, is normally the cheapest route per tonne once you are above roughly five tonnes. It needs somewhere to tip, and it needs moving before it sets into a heap. Small 25 kg bags are convenient for borders, topping up existing gravel, or anywhere a lorry cannot reach, and expensive for anything else.
As a rough 2026 guide: a bulk bag of 20mm gravel delivered typically lands somewhere around £65 to £95, decorative slate nearer £90 to £130, and loose tipped bulk loads around £45 to £65 per tonne. Regional variation and delivery charges move all of these, so get two quotes.
Takeaway: convert every quote to a price per tonne before comparing merchants.
Planning and drainage
Gravel has one advantage that block paving and tarmac do not. It is permeable. Under the 2008 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. A loose gravel surface over a permeable build-up generally avoids that requirement.
That is not a blanket exemption. Listed buildings, conservation areas and properties with existing planning conditions all change the picture, and Scotland, Wales and Northern Ireland handle this separately. A phone call to the local planning department costs nothing.
Takeaway: gravel is usually the simplest driveway surface to install without an application, but confirm your own case before you order.
Disclaimer
This guide is for general planning and budgeting. It is not a substitute for advice from a qualified groundworker or your local building control department. Ground conditions, drainage requirements and planning rules vary by site and by authority. Confirm quantities and build-up with your supplier and contractor before ordering.