Gravel Calculator – How Much Gravel Do I Need?
Measure your area, pick what you're doing, and we'll work out the tonnes, the bulk bags and roughly what it will cost.
Gravel & Chippings Calculator
What are you doing?
75mm over a compacted MOT Type 1 sub-base. Any deeper and tyres plough through it; any shallower and the base shows through.
Measure rectangles length by width. Split an L-shape into two rectangles, or measure a circle straight across its widest point.
Measure your area
15 m²
Odd-shaped garden? Split it into rectangles, triangles and circles — we add them up for you.
You need
1.77tonnes
15 m² at 75mm deep, including 5% waste
- Volume
- 1.13 m³
- 850kg bulk bags
- 3
- 20kg bags
- 89
- Area covered
- 15 m²
How we worked this out
Your shopping list
3 × 850kg bulk bags of gravel
Delivered on a pallet or crane-offloaded — check access before ordering.
£255
2 × rolls of weed membrane (1m × 10m)
Overlap joints by 100mm and peg every metre.
£50.00
How much does 1 tonne of gravel cover?
| Depth | Coverage per tonne | Coverage per 850kg bulk bag |
|---|---|---|
| 30mm | 22.2 m² | 18.9 m² |
| 40mm | 16.7 m² | 14.2 m² |
| 50mm | 13.3 m² | 11.3 m² |
| 75mm | 8.9 m² | 7.6 m² |
| 100mm | 6.7 m² | 5.7 m² |
How this calculator works
The maths is simpler than it looks. First we work out the area of every section you add — length × width for a rectangle, base × height ÷ 2 for a triangle, π × radius² for a circle — and add them together. Then we multiply that total area by the depth in metres to get a volume in cubic metres.
Volume alone doesn't help at the merchant, because gravel is sold by weight. So we multiply the volume by the density, which for most UK decorative aggregates is about 1.5 tonnes per cubic metre. Finally we add a 5% waste allowance for spreading, settling and topping up, then divide by the bag weight and round up — because no merchant sells you 0.7 of a bulk bag.
In short: area (m²) × depth (m) × 1.5 = tonnes, then tonnes ÷ 0.85 = 850kg bulk bags.
Worked example: a 5m × 3m driveway
Say you're gravelling a single driveway measuring 5m long by 3m wide. That's 15m². At the driveway depth of 75mm, the volume is 15 × 0.075 = 1.125m³. Multiply by 1.5 and you get 1.69 tonnes. Add 5% waste and you're at 1.77 tonnes, which is three 850kg bulk bags — or two bags if you're prepared to run a little thin in places and top up later.
At around £85 a bulk bag delivered, that's roughly £170–£255 of gravel. You'll also need two rolls of 1m × 10m weed membrane at about £25 each. And remember the layer nobody budgets for: 150mm of MOT Type 1 under a driveway means 15 × 0.15 × 2.1 = 4.7 tonnes of sub-base, which usually costs more than the gravel itself.
Tips from the trade counter
- Measure twice, in metres. Use a 30m open-reel tape rather than a 5m pocket tape, and write each measurement down as you go.
- Break odd shapes up. A curved border is easier to measure as two rectangles and a triangle than as one clever shape. Add a section per piece above.
- Bulk bags beat handy bags above about 300kg. A 20kg bag at £5 works out at £250 a tonne; a bulk bag is typically £85–£110 a tonne.
- Check access before you order. A bulk bag weighs the best part of a tonne. If the lorry can't get close, you're barrowing it — and that's two hours you didn't plan for.
- Buy in winter if you can. Aggregate prices tend to be keenest between November and February, when merchants are quiet.
- Angular over rounded for drives. 20mm angular gravel locks together; pea shingle rolls out onto the pavement.
UK rules worth knowing
In England and Wales you can usually lay a new front driveway under permitted development if the surface is permeable — and loose gravel counts. Laying more than 5m² of impermeable surface that drains straight onto the road needs planning permission.
Dropping the kerb to get onto your drive always needs the highway authority's approval, whatever the surface. Rules differ in Scotland and Northern Ireland, and conservation areas and listed buildings have extra restrictions — always check with your local council before you start.
Frequently asked questions
How much gravel do I need for a driveway?
Allow 50–75mm of gravel over a compacted sub-base. A 5m × 3m driveway (15m²) at 75mm needs about 1.7 tonnes, which is two 850kg bulk bags.
How many square metres does a bulk bag of gravel cover?
An 850kg bulk bag covers roughly 14m² at 40mm deep, 11m² at 50mm, or about 7.5m² at 75mm, assuming a density of 1.5 tonnes per cubic metre.
How deep should gravel be?
40–50mm for paths and borders, 50–75mm for driveways, around 70mm for large pebbles and about 100mm for cobbles. Deeper than 80mm on a drive makes steering heavy and pushes stone out of place.
Do I need a membrane under gravel?
Yes. A woven weed membrane stops weeds growing through and keeps the gravel from sinking into the soil or sub-base. It costs very little compared with re-doing the job.
What does 1 tonne of gravel cover?
About 16.7m² at 40mm, 13.3m² at 50mm and 8.9m² at 75mm deep.
Is gravel cheaper in bulk bags or small bags?
Bulk bags are usually less than half the price per tonne. Small 20kg bags only work out cheaper if you need under roughly 300kg or cannot get a delivery lorry to the property.
What size gravel is best for a driveway?
20mm angular gravel. Angular stone locks together and stays put, while rounded pea shingle rolls under tyres and migrates towards the road.
Does the calculator include waste?
Yes — a 5% allowance by default for settling, spreading and topping up. You can change it in Advanced settings.