Gravel Calculator

Start by choosing your units, metres or feet, then enter the length and width of the area you want to cover. For an irregular space, split it into rectangles, calculate each one, and add the results together.

Set the depth of the gravel layer. A 50mm (0.05m) layer suits decorative beds and footpaths, while a driveway that carries vehicles needs 75mm to 100mm over a firm sub-base. Depth matters as much as surface area, so measure it honestly rather than guessing.

Pick a gravel type from the list. Each option sets a typical density, but you can override it: choose Custom density, or simply type your own figure into the density field if your supplier has given you an exact value.

Adjust the extra allowance if you want more or less buffer than the default 5 percent, and enter a price per tonne to see a cost estimate. Everything updates live as you type, so there is no submit button to press.

The maths behind gravel quantities is straightforward geometry followed by a density conversion. First the calculator works out the volume: length times width times depth. When you enter feet, each dimension is converted to metres first (one foot is 0.3048 metres), so the volume always comes out in cubic metres.

Next it converts volume into weight. Gravel is sold by the tonne, so the calculator multiplies the volume in cubic metres by the density in tonnes per cubic metre. A typical loose gravel density is 1.5 tonnes per cubic metre, but the real figure ranges from about 1.4 for light pea gravel up to 1.7 for a compacted gravel and sand mix.

The waste allowance is then applied by multiplying the weight by one plus the allowance percentage. With the default 5 percent, a result of 1 tonne becomes 1.05 tonnes. Finally, the calculator divides the total tonnage by 0.85, the weight of a standard bulk bag, and rounds up to whole bags, because suppliers do not sell part bags.

As a worked example, a 5m by 3m bed at 0.05m deep gives 0.75 cubic metres. At 1.5 tonnes per cubic metre with no waste that is 1.13 tonnes, which rounds up to 2 bulk bags. Add the default 5 percent allowance and the tonnage rises to about 1.18 tonnes.

The headline figure is the tonnes needed, including your waste allowance. This is the number to give a supplier when ordering loose tipped gravel, which is usually the cheapest option for larger driveways and paths.

The volume in cubic metres is shown before waste, so you can compare it against quotes that price by volume rather than weight. It is also a useful sanity check: if the volume looks far too large or small, re-check your depth, since a value entered in millimetres instead of metres is the most common mistake.

The bulk bags figure tells you how many tonne bags to order if you prefer bagged delivery. Bags are easier to move and store but cost more per tonne than loose gravel. The estimated cost appears once you enter a price per tonne, multiplying your total tonnage by that rate. These are planning estimates; always confirm exact quantities and prices with your supplier before you order.