Free calculator
Topsoil Calculator
Calculate topsoil volume from area and depth, then match the result to the supplier bag or bulk specification.
Open calculator →Garden material maths reference
Garden material depth & volume reference
Use this table when you already know the depth you want and simply need to see what that depth means in litres or cubic metres.
volume (m³) = area (m²) × depth (m) · 1mm over 1m² = 1 litre
Litres per square metre
Depth translates directly into litres per m²
This table is mathematical. It does not recommend a horticultural or construction depth for any particular material.
| Selected depth | Litres per m² | 10m² | 20m² | 50m² | 100m² |
|---|---|---|---|---|---|
| 1mm | 1L | 10L | 20L | 50L | 100L |
| 5mm | 5L | 50L | 100L | 250L | 500L |
| 10mm | 10L | 100L | 200L | 500L | 1,000L |
| 25mm | 25L | 250L | 500L | 1,250L | 2,500L |
| 50mm | 50L | 500L | 1,000L | 2,500L | 5,000L |
| 75mm | 75L | 750L | 1,500L | 3,750L | 7,500L |
| 100mm | 100L | 1,000L | 2,000L | 5,000L | 10,000L |
Worked depth-to-volume examples
20m² at 50mm
20 × 0.05 = 1.00m³That is 1,000 litres before any separate ordering allowance.
60m² at 3mm
60 × 0.003 = 0.18m³That is 180 litres — a useful way to think about a shallow lawn topdressing.
30m² at 75mm
30 × 0.075 = 2.25m³That is 2,250 litres. Weight still depends on the material density.
20m² at 100mm
20 × 0.10 = 2.00m³That is 2,000 litres of finished geometric volume.
Volume is not automatically weight
Topsoil, gravel, bark, compost and sub-base can all occupy the same cubic metre but weigh very different amounts. Moisture, particle size, composition and compaction alter bulk density. Calculate the space first; use the supplier's density or stated pack specification only when a weight conversion is actually needed.
Finished depth is not always order volume
A compacted sub-base layer, a settled soil layer and a loose bark layer can each need different purchasing logic. The table above gives the finished geometric volume only. If the material is expected to compact, settle or be bought with a separate allowance, keep that extra factor visible rather than hiding it inside the depth.
Choose the depth in the project guide, not this table
This page deliberately does not say that 50mm is “the right depth” for gravel, mulch, topsoil or any other material. Use the relevant calculator and guide to decide the project input, then come back here when you only need to verify the arithmetic.
Use the material-specific calculator next
Different materials share the volume maths but not the purchasing assumptions.
Free calculator
Mulch Calculator
Calculate organic mulch volume for beds and borders from measured area and chosen depth.
Open calculator →Free calculator
Gravel Calculator
Estimate gravel volume, approximate weight and bags from area, depth and editable density.
Open calculator →Free calculator
Lawn Topdressing Calculator
Calculate a shallow lawn dressing in litres, cubic metres and bags without confusing it with deeper topsoil work.
Open calculator →Free calculator
Patio Materials Calculator
Estimate paving, compacted sub-base, bedding and optional simple jointing quantities for a patio build-up.
Open calculator →Free calculator
Bark Calculator
Plan bark chippings or woodchip by volume, bags and an optional existing-layer top-up.
Open calculator →