How to work out how much gravel or mulch you need
- Choose Gravel or stone or Mulch, bark or soil, and feet or metres.
- Enter the Length and Width of the area and the Depth you want to fill: 2 to 3 in (5 to 7.5 cm) for paths and mulch beds, 4 in (10 cm) or more for driveways.
- Read the volume in cubic yards or cubic metres. For gravel you also get the weight range in tonnes and US tons; for mulch, the number of bags.
The formula
Volume = length × width × depth, with everything in the same unit. In feet: 20 × 10 × (3 ÷ 12) = 50 cubic feet, and 50 ÷ 27 = 1.85 cubic yards, since a cubic yard is 3 × 3 × 3 = 27 cubic feet. In metres: 6 × 3 × 0.075 = 1.35 m³.
Gravel weight uses a range of 1.4 to 1.7 tonnes per cubic metre for loose gravel, so 1.35 m³ is about 1.9 to 2.3 tonnes.
Ordering tips
- Round up. Suppliers usually sell in half or whole cubic yards (or tonnes), and gravel settles once it’s raked and compacted. Ordering 5 to 10% more avoids a second delivery.
- Bulk or bags? For more than about a cubic yard, bulk delivery is usually cheaper than bags, but you’ll need space for the pile.
- Round beds. Work out the area as 3.14 × radius × radius, then enter it as the length with a width of 1. A bed 8 ft across has a radius of 4 ft and an area of about 50 sq ft.
For a concrete slab or footing, the concrete calculator works out volume and premix bags.