Gravel Calculator — Bags and Weight for Paths and Driveways
Gravel is sold by weight, so you need to know both the volume and the density of the stone you are buying. This calculator converts your area and depth into cubic metres, then into kilograms and bags — so you can order the right amount without guesswork.
How we calculate
Volume = length × width × depth (m) × (1 + waste %). Weight = volume × density. Bags = ⌈weight ÷ bag weight⌉.
Worked example
5 m × 3 m at 50 mm: volume = 0.75 m³ × 1.1 = 0.825 m³. At 1,500 kg/m³: 1,238 kg. At 25 kg/bag: ⌈1,238 ÷ 25⌉ = 50 bags.
Common mistakes
- Using the wrong density — different stone types (pea gravel, slate chips, crushed granite) vary significantly.
- Not laying a weed membrane first — gravel paths need a barrier or weeds push through within months.
- Skipping an edging restraint — loose gravel migrates onto lawns and paths without containment.
- Ordering bags when bulk tonne bags cost far less per kg for areas larger than about 10 m².
Frequently asked questions
How deep should gravel be for a garden path?+
A decorative garden path needs 40–50 mm of gravel. For a driveway with light vehicle traffic, use at least 75–100 mm. Laying on a compacted sub-base and weed membrane first ensures the gravel stays in place longer.
How many bags of gravel do I need per square metre?+
At 50 mm depth with a density of 1,500 kg/m³, one square metre needs about 75 kg — roughly 3 bags at 25 kg each. Deeper layers or denser stone will need more. Use the calculator to adjust for your specific depth and stone type.
What is the difference between pea gravel and crushed gravel?+
Pea gravel is smooth and rounded, making it comfortable underfoot and good for decorative areas. Crushed gravel has angular edges that lock together under traffic, making it better for driveways and parking areas. Density varies slightly between types.
Do I need a weed membrane under gravel?+
Yes, for any gravel path or bed that you want to stay weed-free. A permeable landscape fabric lets water through while blocking light from reaching weed seeds in the soil below. Without it, weeds will push through within a season.