Decorative stone is sold by weight but covers ground by volume, which is why nobody can ever work out how much to buy. Enter the area and depth and this calculator converts to litres and tonnes, then prices the cheapest way to get it — 25kg handy bags against maxi and bulk bags.
Cobbles and pebbles need laying deeper than fine gravel because of their size: allow 40–50mm so the ground stays hidden when they settle. The engine rounds up to whole bags and shows the trade-offs side by side.
01 — The Calculator
Pick a material, pace out your plot, and the value engine prices every way to fill it — hippo bags, dumpy bags or handy sacks.
Enter dimensions to calculate.
Volume
0 litres
Cubic
0.00 m³
Area
0.0 m²
Est. weight
0.00 tonnes
Best price
—
5 cm
Depth changes the volume a lot — 5cm mulch is normal, raised veg beds want 20cm+.
Not sure? See the depth guide belowEnter your plot dimensions and the value engine will price the cheapest way to cover it.
Worked example: 10m² feature bed at 40mm
A 10m² bed dressed 40mm deep with cobbles needs 400 litres — about 16 × 25kg handy bags at roughly £104, or a part-filled maxi bag if you can use the rest elsewhere. Larger areas quickly tip in favour of a bulk bag; the calculator shows exactly where that tipping point falls for your job.
40–50mm for cobbles and large pebbles (about twice the stone size) so soil doesn't show through when they shift. Fine 10–20mm chippings can go at 30–40mm. Anything deeper is wasted money.
Garden Calculator — Project
My garden project · 29 September 2026
| Item | Qty | Each | Total |
|---|---|---|---|
| Estimated total | £0.00 | ||
Prices from the Garden Calculator sample trade catalogue — confirm with your merchant before ordering.