Soil and Mulch Volume Calculator

1. Enter the length and width of the bed in metres.
2. Enter the depth you want to fill or top up, in centimetres.
3. Choose the material so the weight estimate is right.
4. Set your bag size, then read the volume, bags needed and weight.

A soil volume calculator tells you how much soil, compost, mulch or gravel you need to fill a bed to a given depth. Buying by guesswork leaves you short mid-job or with heavy bags left over, so a quick volume estimate saves both money and trips to the garden centre.

Landscaping materials are sold by volume, in litres, bags or cubic metres, so working out the volume of your bed is the first step in ordering the right amount.

1. Multiply length by width for the surface area in square metres.
2. Multiply by the depth in metres to get the volume in cubic metres.
3. Multiply cubic metres by 1000 for litres.
4. Divide litres by your bag size and round up for the number of bags.

Because depth is entered in centimetres, the calculator divides it by 100 to convert to metres before multiplying, so every unit lines up.

You are filling a border bed 3 metres long and 2 metres wide with 10 centimetres of topsoil. The area is 6 square metres, and at 0.10 metres deep the volume is 0.6 cubic metres, or 600 litres. In 50 litre bags that is 12 bags. As topsoil weighs about 1.3 kilograms per litre, the load is roughly 780 kilograms, worth knowing before it is delivered to your driveway.

Depth

Depth scales the volume directly, so a small change in depth across a large bed adds up to a lot of extra material.

Bed Area

Longer and wider beds need proportionally more, and irregular shapes should be split into rectangles and added together.

Material Type

Volume is the same for any material, but weight varies a lot: gravel is roughly four times heavier than bark mulch for the same volume.

Settling and Compaction

Loose compost and mulch settle over time, so ordering a little extra keeps the finished depth on target.

All these fill the same volume, but they weigh very differently.

For reference, one cubic metre is 1000 litres, and one cubic yard is about 765 litres, if your supplier quotes in yards.

Filling Raised Beds

Work out the exact soil and compost to fill new beds to the brim.

Mulching Borders

Estimate the mulch for a season top-up at a consistent depth.

Ordering in Bulk

Convert your beds into cubic metres so a bulk delivery matches what you need.

1. Forgetting Depth Units

Mixing centimetres and metres throws the volume out by a factor of a hundred; keep depth in centimetres here.

2. Ignoring Settling

Loose materials settle, so a bed filled exactly to volume can sink below the edge later.

3. Buying by Weight Alone

Bags are sold by litres, not kilograms, so compare volume, not weight, when ordering.

4. Treating Odd Shapes as One Rectangle

Split L-shaped or curved beds into simple rectangles and add the volumes.

The volume maths is exact for a rectangular bed, and weights use typical densities. Real densities vary with moisture and product, so treat weight as an estimate.

Multiply length by width by depth. A 3 by 2 metre bed at 10 cm deep needs 0.6 cubic metres, or 600 litres, of soil.

A cubic metre is 1000 litres, so it is 20 bags of 50 litres, or about 40 bags of 25 litres.

Mulch is usually 5 to 8 cm deep, topsoil for beds around 10 to 15 cm, and raised beds are filled to their full height, often 20 to 30 cm.

Use the same volume formula: area times depth. For mulch, a 5 to 8 cm depth is typical, which suppresses weeds without smothering plants.

Topsoil is about 1.3 kg per litre, compost about 0.7, bark mulch about 0.4 and gravel about 1.6, though moisture changes these figures.

One cubic yard is about 765 litres, or 0.765 cubic metres, if your supplier quotes bulk material in yards.

Split it into rectangles and add the volumes, or for a circle use pi times the radius squared times the depth.

A little extra allows for settling and uneven ground, so rounding up by five to ten percent is sensible for loose materials.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Volume of a cuboid (Wikipedia).
• Topsoil and garden soil (Wikipedia).
• Mulch in gardening (Wikipedia).