About this calculator
Landscaping a bed, a path or a driveway? Enter the area in metres and the depth in millimetres, pick the material, and get the volume to order, the weight in tonnes and the number of bulk bags.
A 10% allowance is added by default for settling and uneven ground. Weights use typical densities, so check with your supplier.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
5 m × 4 m of gravel, 50 mm deep
- Gravel to order
- 1.1 m³ (about 1.76 tonnes)
- Exact volume
- 1 m³
- Weight with the extra
- 1.76 tonnes
- Bulk bags (0.85 m³ each)
- 2
- Litres
- 1,100
A 5 m × 4 m area covered 50 mm deep needs 1.1 m³ of gravel, about 1.76 tonnes, including 10% extra.
Show the working
- Volume = length × width × depth = 5 × 4 × 0.05 m = 1 m³.
- Add 10% for settling and uneven ground: 1.1 m³.
- Weight = volume × density; gravel is about 1.6 tonnes per m³ (a typical figure: it varies with moisture and grade, so check your supplier). Bulk bags are usually about 0.85 m³.
Bark mulch for a 10 m × 2 m border, 75 mm
- Bark mulch to order
- 1.65 m³ (about 0.58 tonnes)
- Exact volume
- 1.5 m³
- Weight with the extra
- 0.58 tonnes
- Bulk bags (0.85 m³ each)
- 2
- Litres
- 1,650
A 10 m × 2 m area covered 75 mm deep needs 1.65 m³ of bark mulch, about 0.58 tonnes, including 10% extra.
Show the working
- Volume = length × width × depth = 10 × 2 × 0.075 m = 1.5 m³.
- Add 10% for settling and uneven ground: 1.65 m³.
- Weight = volume × density; bark mulch is about 0.35 tonnes per m³ (a typical figure: it varies with moisture and grade, so check your supplier). Bulk bags are usually about 0.85 m³.
Topsoil for a 6 m × 3 m lawn, 100 mm
- Topsoil to order
- 1.98 m³ (about 2.57 tonnes)
- Exact volume
- 1.8 m³
- Weight with the extra
- 2.57 tonnes
- Bulk bags (0.85 m³ each)
- 3
- Litres
- 1,980
A 6 m × 3 m area covered 100 mm deep needs 1.98 m³ of topsoil, about 2.57 tonnes, including 10% extra.
Show the working
- Volume = length × width × depth = 6 × 3 × 0.1 m = 1.8 m³.
- Add 10% for settling and uneven ground: 1.98 m³.
- Weight = volume × density; topsoil is about 1.3 tonnes per m³ (a typical figure: it varies with moisture and grade, so check your supplier). Bulk bags are usually about 0.85 m³.
How it's worked out
Volume = length × width × depth (in metres). The extra allowance is added, then the volume is multiplied by the material's density to give the weight. A bulk bag holds about 0.85 m³.
Typical densities and depths
- Gravel and aggregate: about 1.6 tonnes per m³; 40 to 50 mm for a path, 50 to 75 mm for a drive
- Topsoil: about 1.3 t/m³; 100 to 150 mm for a lawn
- Sand: about 1.6 t/m³
- Bark mulch: about 0.35 t/m³; 50 to 75 mm around plants
- Compost: about 0.5 t/m³
Order tips
Loose loads are sold by the tonne or cubic metre, bagged material by the bag. Wet material weighs more than dry. Compare the weight with the lorry or bag capacity, and if the ground is soft or uneven, add more than 10%.
Frequently asked questions
How do I calculate how much gravel I need?
Multiply length by width by depth in metres, add 10%, then multiply by about 1.6 for tonnes.
How deep should gravel be?
About 40 to 50 mm for a path and 50 to 75 mm for a driveway, over a sub-base.
How many tonnes in a cubic metre?
It depends on the material: roughly 1.6 for gravel, 1.3 for topsoil, 0.35 for bark.
What is a bulk bag?
A large bag, usually about 0.85 m³ (roughly a tonne of aggregate).
Why add 10%?
Material settles and ground is rarely perfectly level.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.