How to Calculate Topsoil
Use a simple area × depth calculation to estimate topsoil volume for garden beds, lawns and planting areas.
1. Measure the area
Measure the length and width of a rectangular area in metres. For an irregular space, divide it into simple sections, calculate each section and add the results.
2. Choose the average topsoil depth
Decide how deep the new topsoil layer should be for the project. Measure uneven areas in several places and use a sensible average rather than one unusually deep or shallow point.
3. Use the topsoil formula
Topsoil volume (m³) = length × width × depth (m).
If depth is given in centimetres, divide it by 100 before using the formula. For example, 10 cm = 0.10 m.
4. Convert cubic metres to litres
One cubic metre contains 1,000 litres. So 1.5 m³ is 1,500 litres. This makes it easier to compare a bulk estimate with bagged topsoil.
Worked example
A 5 m × 3 m area at 10 cm depth gives 5 × 3 × 0.10 = 1.5 m³. With a 5% planning allowance, 1.5 × 1.05 = 1.575 m³.
Topsoil for lawns and garden beds
For lawns, calculate the area receiving the new layer rather than the entire property. For garden beds, exclude sections that will be filled with other materials such as drainage layers or decorative mulch.
How much extra topsoil should I order?
An allowance can account for small measuring differences, trimming and settling. The right percentage depends on the site and product. If a supplier gives a specific ordering recommendation, use that information.
Bagged topsoil versus bulk delivery
Bulk soil is commonly discussed in cubic metres, while bags are often sold in litres. Divide the required litres by the bag size to estimate the number of bags, then round up to whole bags.
Common mistakes
- Forgetting to convert centimetres to metres.
- Using the full bed height when another material occupies part of the space.
- Using one depth measurement on an uneven area.
- Assuming a universal soil density when the supplier provides different product information.
Use the calculator
Enter your measurements in the Topsoil Calculator →. You can also compare the result with the Soil Calculator → and Volume Calculator →.
Frequently asked questions
What is the formula for topsoil?
For a simple rectangular area, multiply length × width × depth in metres to get cubic metres.
How many litres are in 2 cubic metres?
2 m³ equals 2,000 litres.
Can I calculate an irregular garden?
Yes. Split the garden into rectangles or other simple measurable sections, calculate each one and add the volumes.