Stone Calculator
Find the tonnes and bags of decorative or garden stone you need. It works for gabion baskets too.
Measure your project
Your answer
That is 0.60 m³.
If you buy bags
If you buy bulk bags
A gabion wall or a drive holds weight. Check your local building rules or ask a builder or engineer.
What it costs
£107 a bulk bag, with VAT, is the middle of only 3 sellers (Oct 2026). Gravelmaster's price, the middle one, includes delivery. Treat it as a rough guide.
Quick answers
- A 4 × 3 m border, 50 mm deep
- About 0.99 tonnes of Cotswold chippings. That is 2 bulk bags of 850 kg.
- Stone weight per m³
- Cotswold chippings about 1.65 tonnes, gravel and slate 1.6, and pea gravel 1.5.
- What 1 tonne covers
- About 12 m² of Cotswold chippings at 50 mm deep, or 24 m² at 25 mm.
- Gabion stone
- About 1.6–1.7 tonnes for each 1 m³ of basket. That is about 2 bulk bags of 850 kg.
How to work it out
- Pick your stone. Each one weighs a little more or less per m³.
- Measure the length and width in metres. Length × width gives m².
- Change the depth to metres: mm ÷ 1,000. For a gabion, use the basket height.
- m² × depth gives the volume of stone in m³.
- Multiply by the weight of 1 m³ to get tonnes. For Cotswold chippings, that is 1.65.
- Divide the tonnes by 0.85 to get bulk bags of 850 kg. Round up.
4 × 3 × 0.05 = 0.6 m³
0.6 × 1.65 = 0.99 tonnes
0.99 ÷ 0.85 = 1.2 → 2 bulk bags
Stone weight calculator: tonnes per m³
Stone is sold by weight, but you fill a space. So you need the weight of 1 m³. These come from UK sellers and quarries.
| Stone | Tonnes per m³ | Who says |
|---|---|---|
| Cotswold chippings | 1.65 | Natural Stone & Timber (Gilmore's cover gives 1.7) |
| Decorative gravel, 20 mm | 1.6 | Wickes |
| Slate chippings | 1.6 | Wickes; Berwyn Slate agrees |
| Pea gravel, 10 mm | 1.5 | Gravel Base, a supplier |
| Gabion stone, per m³ of basket | 1.6–1.7 | Mainland Aggregates; Smiths quarry |
From sellers' cover figures, as laid. The gabion row is per m³ of basket.
For builders' stone, such as MOT Type 1 (made to a road standard), see our aggregate calculator.
Stone coverage: what a tonne or a bulk bag covers
Lighter stone covers more ground per tonne. Pick the depth, then read across.
| Stone | 1 tonne, 25 mm | 1 tonne, 50 mm | 850 kg bag, 50 mm |
|---|---|---|---|
| Cotswold chippings | 24.2 m² | 12.1 m² | 10.3 m² |
| Decorative gravel (20 mm) | 25 m² | 12.5 m² | 10.6 m² |
| Slate chippings | 25 m² | 12.5 m² | 10.6 m² |
| Pea gravel (10 mm) | 26.7 m² | 13.3 m² | 11.3 m² |
Gilmore's own cover is close. It says 850 kg of Cotswold chippings covers 10 m² at 50 mm. At 25 mm, it says 420 kg.
Gabion stone calculator: rock for baskets
A gabion is a wire basket filled with rock. Work out the basket's volume: length × width × height, in metres.
Then allow 1.6–1.7 tonnes of rock for each m³. Smiths quarry says 1.7, and Mainland Aggregates says 1.6.
| Basket | m³ | Tonnes | 850 kg bags |
|---|---|---|---|
| 1 × 1 × 1 m | 1 | 1.60–1.70 | 2 |
| 2 × 1 × 1 m | 2 | 3.20–3.40 | 4 |
| 1 × 0.5 × 0.5 m | 0.25 | 0.40–0.43 | 1 |
| 2 × 0.5 × 0.5 m | 0.5 | 0.80–0.85 | 1 |
Example sizes. Bags use the higher weight, 1.7 tonnes per m³.
- Size: 100–200 mm is the most common at Smiths. Mainland sells 75–200 mm granite.
- Bags: Mainland says one 850 kg bag fills about 0.6 m³ of basket. By its own 1.6 tonnes per m³, it would fill about 0.53 m³.
- Dust: Mainland's stone comes unwashed, with 5–10% fine bits.
A gabion wall holds weight. Check your local building rules or ask a builder or engineer.
Small bags or bulk bags of garden stone?
Small bags are easy to carry, but they cost more per tonne. Gilmore sells Cotswold chippings both ways:
- 20 kg bag: £4.08 with VAT, about £204 a tonne.
- 850 kg bulk bag: £85.14 with VAT, about £100 a tonne.
Gilmore shows its prices without VAT, so we added 20%. Other bulk bags: Natural Stone & Timber £108 with VAT, and Gravelmaster £107 with VAT and delivery.
Gravelmaster sells Cotswold chippings in 20 kg bags and half bags of about 500 kg (£91). Its bulk bags are about 850 kg (£107) or 1,000 kg (£116).
For 1 m² at 50 mm, you need 5 small bags of 20 kg. Ten m² takes 42 small bags, or 1 bulk bag.
Building a drive?
A drive needs a packed base of Type 1 under the top stone. Mainland Aggregates says don't use 6 or 10 mm gravel on a drive, and pea gravel is 10 mm. Our gravel driveway calculator works out both layers.
For slate, see the slate chippings calculator. For plain gravel paths, see the gravel calculator.
Questions people ask
How much stone do I need?
Multiply the area in m² by the depth in metres, then by the weight of 1 m³. A 4 × 3 m border of Cotswold chippings, 50 mm deep, takes about 0.99 tonnes.
How many bags of stones do I need?
At 50 mm deep, 1 m² takes about 83 kg of Cotswold chippings. That is 5 small bags of 20 kg. One 850 kg bulk bag covers about 10 m².
How many tonnes of stone do I need for a gabion?
Smiths quarry says a 1 m³ basket takes about 1.7 tonnes of stone. Mainland Aggregates says about 1.6. So multiply the basket's m³ by 1.7 to be safe.
What size stone do you put in gabions?
Smiths says 100–200 mm stone is the most common. It also sells 75–150 mm. Mainland sells 75–200 mm granite.
How much does a tonne of decorative stone cover?
About 12.1 m² of Cotswold chippings at 50 mm, or 12.5 m² of slate or gravel. Lighter pea gravel goes a bit further: about 13.3 m².
How deep should decorative stone be?
Gilmore, a builders' merchant, says about 25 mm for borders and paths. For drives and heavy use, it says at least 50 mm. JT Atkinson gives 40–50 mm of gravel for paths.
How heavy is a cubic metre of stone?
It depends on the stone. Cotswold chippings are about 1.65 tonnes per m³, 20 mm gravel and slate about 1.6, and pea gravel about 1.5.
Where our numbers come from
- Cotswold chippings 1.65 t/m³: Natural Stone & Timber
- Cotswold chippings cover per bag: Gilmore Building Supplies
- Cotswold chippings bag sizes and price: Gravelmaster
- Gravel weight: Wickes UK 20 mm gravel bulk bag (800 kg covers 20 m² at 25 mm)
- Small bags: Wickes Major Bags (22.5 kg sand, 22.5 kg gravel)
- Bulk bag prices: the middle price from 3 UK sellers each (Wickes, Tippers, Lawsons; Oct 2026)
- Slate weight: Wickes 20 mm slate chippings bulk bag
- Slate bulk bag covers 10 m² at 50 mm: Berwyn Slate quarry
- Slate chippings price: the middle of 4 prices from only 2 UK sellers (Wickes, Tippers; Oct 2026, with VAT)
- Slate chippings 20 kg bag: Wickes Major Bag £10
- Pea gravel weight 1.5 t/m³: Gravel Base supplier
- Pea gravel small bag: Wickes 10 mm Major Bag £4.10
- Pea gravel 850 kg bulk bag: TW Aggregates £46.80
- Pea gravel 850 kg bulk bag: JT Atkinson £70.21
- Pea gravel 850 kg bulk bag: Turnbull £78.66
- Pea shingle 800 kg bulk bags on B&Q (marketplace seller)
- Gabion basket needs about 1.7 t per m³: Smiths quarry
- Gabion stone 1.6 t/m³: Mainland Aggregates Celtic stone
- Mainland Aggregates: 850 kg bulk bags
- JT Atkinson: gravel depth guide
- Mainland Aggregates: gravel driveway guide
- Pea gravel bulk bag covers about 12 m²: Heidelberg data sheet
- Type 1 vs crusher run: Lightwater Quarries
Made by BuildersCount. Last checked 4 Oct 2026.
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