Question 1

How much does topsoil weigh per m³?

Accepted Answer

Screened topsoil typically weighs around 1.4 tonnes per cubic metre, though this can vary between 1.3-1.5 tonnes depending on moisture content and composition. Wet topsoil can weigh significantly more. This topsoil quantity calculator uses 1.4 tonnes per m³ as the standard UK trade density for screened topsoil.

Question 2

How deep should I lay topsoil for a new lawn?

Accepted Answer

For a new lawn, you should aim for a minimum of 150mm (6 inches) of topsoil. For best results, 200-300mm is recommended. If you are laying turf, 100-150mm may suffice over existing reasonable soil — use our Turf Calculator to work out how many rolls you need. For flower beds and raised beds, 300mm or deeper is ideal — see our Raised Bed Soil Calculator.

Question 3

How much topsoil is in a bulk bag?

Accepted Answer

A standard bulk bag (also called a tonne bag or dumpy bag) typically holds between 0.6 m³ and 0.75 m³ of topsoil, weighing roughly 0.85-1 tonne. Sizes vary by supplier — Rolawn bulk bags are 730 litres (0.73 m³), while many builders' merchants supply 0.6 m³ bags, so always confirm the exact volume before ordering. This calculator defaults to 0.75 m³ per bag but you can change it in Advanced Options to match your supplier, and it converts volume to bulk bags automatically.

Question 4

How do I calculate topsoil for an L-shaped garden?

Accepted Answer

Split the shape into rectangles, run the calculator once for each rectangle and add the tonnages together. Volumes of loose material are simply additive, so the summed total is exact, not an approximation, and unlike turf or paving there is no cutting penalty where the sections meet. The sections can even use different depths, for example 150mm over a new lawn area and 300mm over a bed. One tip on bags: add the volume figures in m³ first and divide the combined total by your bag size once at the end, because each individual run rounds its bag count up and summing rounded counts can over-order by a bag.

Question 5

What is the difference between topsoil and subsoil?

Accepted Answer

Topsoil is the uppermost layer of soil (typically 150-300mm deep) that contains organic matter and nutrients essential for plant growth. Subsoil sits below and is less fertile with fewer nutrients. For any planting or lawn work, you should always use proper screened topsoil, ideally BS 3882 certified.

Question 6

Should I buy topsoil by the tonne or bulk bag?

Accepted Answer

Bulk bags (usually 0.6-0.75 m³) are convenient for smaller projects and can be placed precisely where needed. For larger areas, buying loose topsoil by the tonne is generally more cost-effective per tonne — as a rule of thumb often noticeably cheaper than the bagged price, though the exact saving varies by supplier and delivery distance, so compare quotes. Most UK suppliers deliver loose topsoil in tipper lorries for orders over 10 tonnes. If you need gravel or sub-base too, see our Gravel Calculator and Type 1 Sub-Base Calculator.

Topsoil Calculator — How Much Topsoil Do I Need?

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