Raised Bed Soil Calculator
Calculate how much soil and compost you need to fill a raised garden bed, with mix breakdowns.
Did this tool work for you?
How to use this calculator
Multiply the bed dimensions to get total volume. The soil mix type determines how that volume is split between topsoil, compost, and perlite.
- 1
Measure your raised bed length and width in metres.
- 2
Enter the bed depth in centimetres.
- 3
Select your preferred soil mix type.
- 4
Read off the total volume, litre requirements, and bag counts for each component.
Frequently asked questions
How does the raised bed soil calculator work out volume?
Volume in cubic metres = length × width × depth in cm ÷ 100, and litres are cubic metres × 1,000. The litre figure is rounded up to a whole litre in the output.
Which soil mixes does it offer?
Three: 100% topsoil; a 60/30/10 blend of 60% compost, 30% vermiculite or perlite and 10% peat or topsoil; and a 50/50 split of compost and topsoil. These are the proportions built into this tool, and other recipes exist.
What does the 60/30/10 option actually split?
The 60% share is labelled compost, the 30% share vermiculite or perlite, and the final 10% peat or topsoil. The tool does not choose between the alternatives for you, so decide which material fills each share before shopping.
What bag size does it assume?
Every bag count uses 40 litre bags, and each material’s litres are divided by 40 and rounded up separately. If your bags hold more or less, divide the litre figure by the size printed on your bags.
Does it include settling or a top-up allowance?
No. The volume is the exact interior box, with no extra for the soil to settle. Add a margin of your own if you want to top up later.
Which dimensions should I enter?
Use the internal length, width and fill depth, in metres and centimetres. Timber thickness reduces the inside size, so measuring outside edges will overstate the volume.
Does it tell me which mix is best for my plants?
No. It splits a volume according to the mix you pick. Nutrient needs, drainage and suitability for particular crops depend on your plants and local conditions.
Soil volume for a raised bed, split by mix
A box of soil in litres
A raised bed is a simple box, so its soil requirement is the product of its three inside dimensions. This calculator multiplies length, width and depth to get cubic metres, converts to litres and then divides that volume among the components of the mix you choose. Each component is counted in 40 litre bags and rounded up, so you know how many to buy of each. The calculation assumes the bed is filled to a single even depth over its full footprint, with vertical sides and no sloping soil at the edges, which suits the usual timber or metal box.
Mix proportions in the code
The table shows how each option divides the total litres between materials.
| Mix option | Compost | Vermiculite / perlite | Topsoil (or peat) |
|---|---|---|---|
| 100% topsoil | 0% | 0% | 100% |
| 60/30/10 blend | 60% | 30% | 10% |
| 50/50 compost and topsoil | 50% | 0% | 50% |
Four beds, as the calculator returned them
The table shows volume, litres and the litres or bags per material for four fixed beds. Material amounts are rounded up to whole litres, as in the tool.
| Bed and mix | Volume | Material litres | Bags of 40 L |
|---|---|---|---|
| 1.2 m × 0.6 m × 30 cm, 60/30/10 | 0.216 m³ (216 L) | Compost 130, perlite 65, topsoil/peat 22 | 4, 2 and 1 |
| 1.2 m × 1.2 m × 20 cm, 60/30/10 | 0.288 m³ (288 L) | Compost 173, perlite 87, topsoil/peat 29 | 5, 3 and 1 |
| 2.4 m × 1.2 m × 30 cm, 50/50 | 0.864 m³ (864 L) | Topsoil 432, compost 432 | 11 and 11 |
| 3 m × 1 m × 25 cm, topsoil | 0.750 m³ (750 L) | Topsoil 750 | 19 |
How rounding shapes the shopping list
In the default bed, 60% of 216 litres is 129.6 litres, which the tool shows as 130 and counts as four 40 litre bags. The tenth share, only 22 litres, still needs a whole bag, so bags can add up to noticeably more than the litre total in small beds. On the larger 2.4 m bed, the 432 litres of each material fit 10.8 bags, which round up to 11. Where you have a choice of bag size, compare the unit price per litre against the extra left over.
Planning around the estimate
Fill volumes rarely match real life exactly, because soil compresses once watered and the bed’s inside dimensions may differ from your plan. Compost and soil are often sold by volume in different units, so convert them to litres before comparing. Choose the blend that suits your plants and local advice; the calculator reports volumes only and makes no recommendation about composition. If you are filling several beds, run each size separately and add the litres, then buy bulk material by the cubic metre where a supplier offers it, since 1,000 litres equals one cubic metre.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →