Topsoil calculator
Work out how much topsoil you need to fill a bed, border or levelling job from its area and depth, so you order the right amount rather than guessing.
Result
Topsoil required
Bags needed (25L)
How to use this calculator
- Measure the length and width of the area to fill, and how deep you need the topsoil layer.
- Enter the three dimensions — switch units if you measured in feet or inches.
- Read the volume required and the equivalent number of standard bags.
Assumptions
- Bag count assumes a standard 25L bag — bulk-bag or loose-load suppliers quote by weight or cubic metre instead.
- Topsoil settles over time, so a freshly filled bed will sit slightly lower after a few weeks — the waste allowance partly covers this.
Technical details: what the fields mean
- Length
length - The longest side of the area to fill.
- Width
width - The other side of the area to fill.
- Depth
depth - How deep a layer of topsoil you want — typically 100–150mm for a new bed or lawn levelling.
- Waste allowance
wastePercent - Extra to cover settling and an uneven sub-base. 10% suits most jobs.
Methodology
Volume = length × width × depth, increased by the waste allowance. Bags assume a standard 25L bag — bulk (loose-tipped) topsoil is usually cheaper for anything over roughly 1m³.
Worked example
3m × 2m bed, 100mm deep, 10% waste
Inputs: length=3, width=2, depth=0.1, wastePercent=10
Result: 0.66 m³ required, 27 bags
Practical guidance
- For anything over about 1m³, ask suppliers for a bulk-bag or loose-tipped price — it's usually much cheaper per litre than bagged topsoil.
- Mix in compost for planting beds — pure topsoil alone is often low in organic matter.
Common mistakes
- Forgetting that topsoil settles and compacts, leaving the bed lower than expected a few weeks later.
- Ordering bagged topsoil for a large area where a bulk bag would be far cheaper.
FAQs
How much topsoil do I need for a 3m x 2m bed?
At 100mm deep with a 10% waste allowance, about 0.66 cubic metres — 27 standard 25L bags.
Is bagged or bulk topsoil cheaper?
Bulk (loose-tipped or bulk-bag) topsoil is almost always cheaper per litre once you need more than about 1 cubic metre.