Gravel Calculator UK

How Much Gravel Do I Need?

Working out how much gravel you need is straightforward once you know the formula. Here is the method landscapers and builders use:

1. Measure your area - for a rectangle, measure the length and width in metres. For a circle, measure the diameter. For example, a typical garden path might be 8m long and 1m wide.
2. Calculate the area - for a rectangle: length × width. For a circle: π × (diameter ÷ 2)². Our example path is 8 × 1 = 8 m².
3. Choose your depth - 50mm is standard for paths and borders. Driveways need 75-100mm. Convert to metres: 50mm = 0.05m.
4. Calculate volume - area × depth in metres. Our path: 8 × 0.05 = 0.4 m³.
5. Add waste - add 5-10% for uneven ground and spreading loss. 0.4 × 1.05 = 0.42 m³.
6. Convert to weight - multiply volume by the gravel density (typically 1,400-1,750 kg/m³). For pea gravel at 1,500 kg/m³: 0.42 × 1,500 = 630 kg = 0.63 tonnes.

For our example path, you would need 1 bulk bag (850kg) or 26 mini bags (25kg each).

Types of Gravel Available in the UK

Choosing the right gravel depends on your project. Here are the most common types available from UK builders' merchants:

Densities are approximate and can vary by 5-10% depending on moisture content and source. When in doubt, ask your supplier for the specific density of the product you are ordering.

How Deep Should Gravel Be?

Getting the depth right is critical - too shallow and the gravel won't last; too deep and it becomes hard to walk or drive on.

Do I Need a Sub-base Under Gravel?

For a long-lasting gravel surface, proper preparation is essential. Here is what goes underneath your gravel:

Weed membrane - lay a heavy-duty woven geotextile membrane over the prepared ground before adding gravel. This prevents weeds growing up through the gravel without blocking drainage. Use a minimum 100g/m² membrane for paths and 120g/m² for driveways. Overlap sheets by at least 150mm and pin with membrane pegs every 300mm along edges.

Sub-base for driveways - a compacted sub-base is essential for driveways to prevent the gravel sinking into soft ground. Use MOT Type 1 (crushed limestone and aggregate graded 0-40mm) at a minimum depth of 100-150mm, compacted with a vibrating plate compactor. For heavy use, increase to 200mm.

Edge restraints - without edging, gravel migrates onto lawns and flower beds. Options include treated timber boards, aluminium lawn edging, brick borders or stone kerbs. For driveways, rigid edge restraints are a must. If you're also putting up a fence alongside your gravel area, the fence posts can double as edge restraints on one side.

Drainage - gravel is naturally free-draining (a major advantage over block paving for planning purposes). However, ensure the sub-base allows water to pass through and that the area has a slight fall (1:80 minimum) to direct surface water away from buildings.

Bulk Bags vs Mini Bags: How to Buy Gravel in the UK

Gravel is sold by weight in the UK, not by volume. Here are the common ways to buy it:

• Bulk bags (850kg) - also called "dumpy bags" or "tonne bags". Despite the name, most bulk bags contain approximately 850kg, not a full tonne. This is the most economical option for larger areas. Delivered by lorry with a grab or HIAB crane. Typical cost: £50-£120 per bag depending on gravel type.
• Mini bags (25kg) - sold at Wickes, B&Q, Screwfix and builders' merchants. Convenient for small areas and easy to transport in a car. Typical cost: £4-£8 per bag. For anything over about 500kg, bulk bags are much cheaper.
• Loose loads - for very large projects (5+ tonnes), loose tipper delivery is the cheapest option. Sold by the tonne. You will need space for the lorry to tip and somewhere to store the pile.

Tip: always order 5-10% more than your calculation shows. You will lose some gravel during spreading and compaction, and it's much easier to use a small surplus than to order a top-up delivery.

How to Save Money on Gravel

Gravel is relatively inexpensive, but waste adds up - especially on larger projects. Here are practical ways to minimise waste:

• Prepare the ground properly - remove soft spots, level the area and compact the sub-base before laying gravel. Uneven ground requires more gravel to fill dips.
• Install edge restraints first - edging prevents gravel spreading beyond the intended area. This is the single biggest cause of gravel waste in gardens.
• Use a weed membrane - membrane prevents gravel sinking into soft soil over time, meaning you won't need to top up as often.
• Spread evenly - use a landscaping rake to distribute gravel to a consistent depth. Dumping and roughly spreading wastes material in high spots.
• Choose the right size - smaller gravel (10mm) compacts better and needs less depth. Larger gravel (40mm) needs a deeper layer to look right and feel stable underfoot.
• Order accurately - use this calculator to work out exactly what you need, then add 5% waste allowance. Over-ordering by "a bag or two to be safe" is the most common source of leftover gravel.