How much topsoil do I need?

Area alone is not enough

When ordering topsoil for a lawn, garden bed or raised bed, you need two measurements: the area and the intended layer depth. A thin surface layer and a deep growing bed over the same area do not use the same amount.

Calculate the topsoil volume

Measure the area that will actually be filled in square metres. For an irregular shape, divide it into smaller rectangles and add them together. If the area has clear slopes or areas of fill, you may need to use more than one layer depth.

Convert the depth to metres: 10 cm = 0.10 m and 25 cm = 0.25 m.

Layer depth depends on the project

A lawn, garden bed and raised bed do not need the same type or depth of soil. Base the choice on plant needs, existing ground, drainage and the product or supplier's guidance.

An unnecessarily thick layer can raise the finished level, cover plant bases or change water flow. Do not add soil to the calculation without first checking what the site and use require.

Litres, cubic metres and order quantity

Topsoil is often sold in bags stated in litres or as loose volume in cubic metres. The unit conversion is exact: 1 m³ = 1,000 l. Check whether the bag volume is a nominal fill volume and whether loose material is measured before or after settling.

Growing medium can settle as it is watered and establishes. The appropriate order allowance depends on the product, finished surface and supplier's way of measuring and delivering it. Measure carefully and ask the supplier if you are unsure how to order.

Quick checks before ordering

• Does the calculated area actually correspond to the area that will be filled?
• Will existing soil be reused, or will it be removed before filling?
• Is the filling depth defined separately, and is it the same everywhere?
• Are you ordering growing medium, topsoil, compost or mulch? These are not the same product.

Once area, layer depth and intended use are clear, you have a calculated volume that can be refined with the supplier's product information.