How it’s worked out
First the volume, then its weight from the material’s density:
Volume = length × width × depth Weight = volume × density Bags = weight ÷ bag weight (rounded up)
Densities vary with the stone, how wet it is and how it settles, so the calculator uses a typical figure for each material, labelled as typical, and lets you type your supplier’s instead.
Worked example
A path 4 m by 3 m with 5 cm of gravel is 0.6 m³. With 5% extra that is 0.63 m³, about 1.01 tonnes at a typical 1.6 t/m³, or 41 bags of 25 kg.
| Material | Typical density, t/m³ | 10 m², 5 cm deep |
|---|---|---|
| Gravel | 1.6 (1.5–1.7) | 0.8 t |
| Sand | 1.6 (1.5–1.7 dry) | 0.8 t |
| Topsoil | 1.3 (1.2–1.5) | 0.65 t |
| Bark mulch | 0.4 (0.25–0.45) | 0.2 t |
How deep?
- Decorative gravel on a path or border: 4–5 cm (about 2 in).
- A gravel driveway: about 5 cm of gravel over a compacted sub-base.
- Bark mulch on beds: 5–7.5 cm (2–3 in).
- Topsoil for a new lawn: 10–15 cm (4–6 in).
How to read the result
- The weight is what you order by from most suppliers; bulk bags usually hold about 0.7–0.85 tonnes.
- Volume is for mulch and compost, which are often sold by the litre or cubic foot.
- In imperial, tons are US tons of 2,000 lb.
Common mistakes
- Typing the depth in metres instead of centimetres: 5 cm is 0.05 m.
- Forgetting that the sub-base settles when compacted: add 10% or more for it.
- Using one density for everything: bark is a quarter of the weight of gravel.
How to use it
- Choose the material.
- Type the length, width and depth.
- Type your bag size to count bags, or your supplier’s density if you have it.
Questions
How much gravel do I need?
Multiply the area by the depth for the volume, then by the density for the weight. A 4 × 3 m path 5 cm deep needs about 1.01 tonnes with 5% extra.
How many bags of gravel in a tonne?
Forty bags of 25 kg make a tonne.
How heavy is a cubic metre of topsoil?
Typically 1.2–1.5 tonnes, heavier when wet; the calculator uses 1.3 unless you type your supplier’s figure.
More calculators
See all 39 calculators. Everything runs in your browser; nothing you type is sent anywhere.