Quick answer: Each square metre of gravel laid 50 mm deep takes 0.05 m³, or 50 litres, which weighs about 80 kg at a typical 1.6 tonnes per cubic metre. At 40 mm it is about 64 kg per m², and at 25 mm about 40 kg. One tonne covers roughly 12.5 m² at 50 mm.
Gravel is ordered by weight but spread by depth, so the useful figure is kilograms per square metre. This guide gives a calculator, a coverage chart and depth advice for borders, paths and driveways. It sits alongside our garden measuring guides, and the method is the same one used in the topsoil calculator guide, with a heavier material.
How much gravel do you need per square metre?
Multiply the depth in metres by the density: 0.05 m × 1,600 kg/m³ = 80 kg per square metre at 50 mm. Loose gravel and chippings usually weigh somewhere around 1.5 to 1.7 tonnes per cubic metre, depending on the stone type, its shape and how much moisture it holds. The chart shows both the midpoint and the range.
| Depth | Volume per m² | Weight per m² (1.6 t/m³) | Range (1.5–1.7 t/m³) | Area per tonne (1.6 t/m³) |
|---|---|---|---|---|
| 25 mm (1 in) | 25 L | 40 kg | 37.5–42.5 kg | 25 m² |
| 30 mm (1¼ in) | 30 L | 48 kg | 45–51 kg | 20.8 m² |
| 40 mm (1½ in) | 40 L | 64 kg | 60–68 kg | 15.6 m² |
| 50 mm (2 in) | 50 L | 80 kg | 75–85 kg | 12.5 m² |
| 75 mm (3 in) | 75 L | 120 kg | 112.5–127.5 kg | 8.3 m² |
| 100 mm (4 in) | 100 L | 160 kg | 150–170 kg | 6.25 m² |
The inch figures are rounded for convenience. In imperial terms, a tonne of gravel at 1.6 t/m³ spread 2 inches deep covers about 132 square feet.
Gravel calculator
Enter the area’s length and width in metres, the depth in millimetres and the bag size your supplier sells. Bulk bags vary, from small bags of around 20 kg to jumbo bags of 850 kg or more, so use the figure on the product listing.
Gravel calculator
m m mm kgArea m² → m³ of gravel, about tonnes ( t), or bags
The bag count rounds up to whole bags at the 1.6 t/m³ midpoint. If the area is irregular, work out the square metres first with the area converter and enter a width of 1.
How deep should gravel be?
Decorative areas usually need 25 to 50 mm, while a driveway needs at least 50 mm of 20 mm gravel over a compacted sub-base. Too thin and the membrane shows through; too deep on a path and the stones move underfoot, which makes walking and wheeling bins hard work.
| Use | Gravel depth commonly used | Notes |
|---|---|---|
| Borders and mulch around plants | 25–50 mm | Smaller stone such as 10 mm needs less depth to cover a membrane. |
| Garden paths | 40–50 mm | Lay over a firm, compacted base with edging to hold the stone in. |
| Driveways | At least 50 mm | 20 mm angular gravel over about 150 mm of compacted MOT Type 1. |
The driveway figures follow common UK practice described by Homebuilding & Renovating: 150 mm of MOT Type 1 compacted in layers, then 50 mm of 20 mm gravel, for a total dig of about 200 mm. Soft ground or heavy vehicles may need a deeper sub-base, so take local advice for anything beyond a household car.
Worked examples
A two-car driveway
A driveway 6 m long and 5 m wide is 30 m². At 50 mm that is 30 × 0.05 = 1.5 m³ of gravel. At 1.6 t/m³ it weighs 2.4 tonnes, with a realistic range of 2.25 to 2.55 tonnes, so three 850 kg bulk bags (2.55 tonnes) would cover it. The sub-base is a separate order: 30 m² × 0.15 m = 4.5 m³ of Type 1, and your supplier can convert that to tonnes for their material.
A side path
A path 12 m long and 0.9 m wide is 10.8 m². At 40 mm it needs 10.8 × 0.04 = 0.432 m³, about 690 kg at 1.6 t/m³. In 20 kg bags that is 34.6, so buy 35. Measuring a long, narrow path accurately matters more than you might think, so check our guide to reading a tape measure if the markings are unfamiliar.
Do you need planning permission for a gravel drive?
In England, gravel is a permeable surface, so surfacing a front garden with gravel does not need planning permission, whatever its size. Since October 2008, paving more than 5 m² of a front garden with an impermeable surface such as concrete or ordinary block paving has needed permission, unless rainwater drains to a lawn or border. The Planning Portal lists gravel, permeable block paving and porous asphalt as options that avoid this. Dropped kerbs, listed buildings and conservation areas have their own rules, and the other UK nations set their own planning rules.
Common mistakes to avoid
- Mixing millimetres and metres. 50 mm is 0.05 m. Entering 50 instead of 0.05 makes the answer 1,000 times too big.
- Confusing stone size with depth. “20 mm gravel” describes the size of the stones, not how thick to lay it.
- Skipping edging. Without a kerb or edging board, gravel migrates onto lawns and pavements and the layer thins.
- Using small rounded pea gravel on a drive. It rolls underfoot and gets carried off in tyre treads; angular stone locks together better.
Bags are usually labelled in kilograms. If a supplier quotes pounds, the kg to lb converter will translate.
Frequently asked questions
How many square metres does a tonne of gravel cover?
At 1.6 tonnes per cubic metre, a tonne covers about 12.5 m² at 50 mm deep, 15.6 m² at 40 mm and 25 m² at 25 mm.
How many 20 kg bags of gravel do I need per square metre?
At 50 mm deep you need about 80 kg per square metre, which is four 20 kg bags. At 25 mm you need about two bags per square metre.
How deep should gravel be on a driveway?
Use at least 50 mm of 20 mm angular gravel on top of about 150 mm of compacted MOT Type 1 sub-base, giving a total depth of around 200 mm.
How much does a cubic metre of gravel weigh?
Loose gravel usually weighs around 1.5 to 1.7 tonnes per cubic metre. The exact figure depends on the stone, its size and shape, and how wet it is.
Does gravel need a membrane underneath?
A permeable landscape membrane is usually laid under decorative gravel and paths to slow weeds and stop the stone mixing into the soil. It lets water drain through, so the surface stays permeable.
Sources
- Paving your front garden: planning permission, Planning Portal
- Permeable surfacing of front gardens: guidance, GOV.UK
- How to lay a gravel driveway, Homebuilding & Renovating
More Garden and Outdoor guides
- How to Measure for a Fence Panel (UK): Panels and Posts
- How to Measure for Artificial Grass: UK Roll Guide
- How Much Gravel Per Square Metre? UK Calculator
- How Much Topsoil Do I Need? UK Calculator and Guide
- How to Measure Lawn Size for Turf (UK Calculator)
- How to Measure a Garden in Square Metres (UK Guide)