How much soil it takes to fill something is each container’s area multiplied by its own fill depth, added together. This tool gives every bed, border and planter its own depth, and reports the total in litres — the unit bagged soil is actually sold in.
A 2 m × 1 m raised bed filled to 40 cm, plus a 6 m × 0.6 m border filled to 25 cm, with 50 L bags.
1,700 litres (L)
| Zone 1 depth | 40 cm |
|---|---|
| Zone 2 depth | 25 cm |
| Bag size | 50 L |
| Improver blend | not entered — no soil and improver split shown |
This is an example, not your result. It matches golden vector S1–S2 in the calculation methodology. Enter your own measurements and select Calculate.
Each container is its own sum: the area of its footprint multiplied by the depth of soil it needs. A 2 m × 1 m raised bed filled to 40 cm holds 0.8 m³, which is 800 litres, or sixteen 50-litre bags. A 6 m border run 0.6 m wide and filled to 25 cm holds another 900 litres. The reason this tool gives every row its own depth is that those two numbers are almost never the same.
Litres lead the result here because that is how bagged soil is sold. Cubic metres are shown alongside, so you can compare a stack of bags against a bulk delivery without doing the conversion in your head.
Filling containers and covering ground are different problems with different failure modes. Filling is bounded — the bed holds what it holds — and the risk is buying a slightly wrong number of bags. Covering is open-ended, and the risk is a delivery you cannot get down the side of the house. If you are ordering by the cubic metre or by the tonne, the topsoil calculator is the right tool, because it handles bulk bags, loose loads and tonnage from a density you supply.
The blend control splits the gross total into two lines that add back up to it: how much soil, and how much improver. It makes no claim about what proportion is right for your plants — that is a horticultural judgement about your soil and what you are growing, and this site does not publish a figure for it.
A freshly filled bed almost always needs more soil within a few weeks. Watering settles the material, air pockets close, and the surface drops. That is normal and it is not something this calculator can predict, because it depends on how compressible your mix is and how it was filled. Buying one bag more than the arithmetic suggests is usually the cheaper mistake.
Every step is arithmetic you can repeat by hand. Full precision is kept through the calculation and rounded once for display.
| Step | Formula |
|---|---|
| Depth to metres | depth m = mm ÷ 1000, or cm ÷ 100, or m × 1 |
| Cubic metres to litres | 1 m³ = 1000 L |
| Circle area | A = π × r², with r = d ÷ 2 when a diameter is entered |
| Gross volume after overage | gross volume = net volume × (1 + overage % ÷ 100) |
| Bag count | bags = ceiling(gross litres ÷ bag litres) |
| Mass from a density you entered | kg = gross m³ × density kg/m³, and tonnes = kg ÷ 1000 |
| Zone volume | zone volume m³ = zone area m² × that zone’s depth m |
| Soil and improver blend split | improver m³ = gross m³ × blend % ÷ 100, and soil m³ = gross m³ − improver m³ |
The calculation methodology sets out every formula, bound and rounding rule this site uses.
SourceRHS — Organic Matter: How to Use in the Garden
https://www.rhs.org.uk/soil-composts-mulches/organic-matter-how-to-use-in-garden