How to use this calculator
- Enter the length and width of the area, or the area itself.
- Enter the depth you want once it is laid.
- Choose the material; the typical density fills in.
- Enter the bag weight to see how many bags to order.
The formula
Volume = area × depth × (1 + extra %)
Weight = volume × density
Bags = weight ÷ bag weight, rounded up
Suppliers often sell by weight (tonnes or tons) but you measure in volume, so density links the two. Typical values: gravel about 1.65 t/m³, sand 1.6, topsoil 1.3, bark mulch 0.35 — all vary with moisture.
Worked example
A 4 m × 3 m area at 50 mm deep, plus 5%, needs 0.63 m³ of gravel.
At 1.65 t/m³ that weighs 1.04 t — 2 bulk bags of 850 kg.
Tips before you buy
- Lay a weed membrane under decorative gravel.
- Check where a delivery lorry can tip or lift a bulk bag before you order.
- Order compacted sub-base (like MOT Type 1) with 15–20 % extra — it shrinks when compacted.
Frequently asked questions
›How much does a cubic metre of gravel weigh?
About 1.5–1.8 tonnes, depending on the stone and how wet it is. We use 1.65 t/m³ unless you change it.
›How many tons of gravel is a cubic yard?
Roughly 1.4 US tons for typical gravel.
›How deep should decorative gravel be?
Usually 40–50 mm (about 2 in). Much deeper and it becomes hard to walk on.
Sources
- Typical bulk densities: aggregate supplier and engineering reference tables (values vary with moisture and grading).
Formulas last reviewed: September 29, 2026. How we check our formulas