Gravel Calculator
Estimate the gravel needed to fill a driveway, path, bed or any area. Choose a rectangle, a circle or a known area, pick the gravel type, and get the volume, tonnage, cubic yards, number of bags and an optional total cost. You can also solve in reverse: enter the tonnage you already have to see how deep it will go.
Formula
Worked example
A driveway 5 m × 3 m (15 m²) at 5 cm deep: 15 × 0.05 = 0.75 m³, plus 10% waste is 0.83 m³. At 1.5 t/m³ that is about 1.24 tonnes. In reverse, 1.5 t at 1.5 t/m³ is 1.0 m³, which over 15 m² spreads to about 6.7 cm deep.
How the gravel calculation works
Gravel is sold by volume or by weight, so an estimate starts with the volume of the space you want to fill. First the calculator works out the area: for a rectangle that is length times width, for a circle it is pi times the radius squared, and if you already know the area you can type it in directly. The area is then multiplied by the depth of the gravel layer to get a cubic volume. The single most common mistake is mixing units, so every dimension is converted to metres before multiplying, a depth entered as 5 cm becomes 0.05 m, which keeps the result honest. Once you have the volume in cubic metres it is converted to cubic yards and cubic feet for suppliers who quote in imperial units.
Turning volume into tonnes, bags and a price
Most aggregate yards sell gravel by the tonne, so the volume is converted into weight using the material density. Density is the mass packed into each cubic metre, and for loose gravel it typically falls between 1.4 and 1.7 tonnes per cubic metre. Rather than guess, pick a gravel type and the calculator applies a sensible density: regular gravel at 1.5, pea gravel and crushed stone nearer 1.6, gravel and sand around 1.7, or type a custom figure from your supplier. A waste allowance of about 10% is added on top, because loose stone compacts once it is spread and rolled. Turn on the cost estimate to price the job: enter a price per tonne, per cubic yard or per bag, set your bag size, and the calculator returns the number of bags and a material total.
Reverse mode and choosing a sensible depth
Sometimes you already have a load of gravel and want to know how far it will go. Switch to reverse mode, enter the tonnage and the area, and the calculator divides the volume across the area to give the achievable depth. This is handy for spreading a delivered bulk bag without ending up too thin. As for depth, the right figure depends on the job. A decorative gravel topping over a weed membrane is usually only 4 to 5 cm so the stones do not scatter underfoot, while a path that takes foot traffic might be 5 to 8 cm. A driveway that carries cars needs a deeper, layered build, often a compacted 10 cm sub-base of larger stone topped with a finer wearing course. Deeper layers multiply the tonnage quickly, so confirm the depth your surface needs before ordering.
Typical gravel depths and densities
| Application | Typical depth | Notes |
|---|---|---|
| Decorative gravel over membrane | 4-5 cm (1.5-2 in) | Keeps stones from scattering |
| Garden path (foot traffic) | 5-8 cm (2-3 in) | Firm underfoot when compacted |
| Driveway sub-base | 10-15 cm (4-6 in) | Layered and rolled for vehicles |
| Regular / dry gravel density | 1.50-1.52 t/m³ | Default 1.5 t/m³ used here |
| Pea gravel / crushed stone | 1.60 t/m³ | A touch denser than rounded gravel |
| Gravel and sand mix | 1.70 t/m³ | Wet material is heavier still |
Use these as starting points; your supplier can confirm the density of a specific aggregate.
Frequently asked questions
How many tonnes of gravel are in a cubic metre?
Loose gravel weighs roughly 1.4 to 1.7 tonnes per cubic metre, so one cubic metre is about 1.5 tonnes on average. The exact figure depends on the stone type, size and how dry it is, which is why the calculator lets you pick a gravel type or enter a custom density.
How much extra gravel should I order?
Add about 10% to the calculated amount, which is the default waste allowance here. Loose gravel compacts when it is spread and rolled, some is lost to spillage, and uneven ground swallows more than a flat plan suggests. The small surplus also lets you top up bare patches later without a second delivery.
Can I calculate gravel for a circle or an irregular area?
Yes. Choose the circle shape and enter the diameter, and the calculator uses pi times the radius squared for the area. For an irregular space, split it into rectangles and circles, calculate each one, and add the volumes, or measure the total area and use the "I already know the area" option.
How do I work out how deep a load of gravel will spread?
Switch the calculator to reverse mode, enter the tonnage you have and the area you want to cover, and it converts the weight to a volume using the density and divides by the area to give the depth in centimetres and inches. If the depth comes out too shallow, order more or cover a smaller area.