Soil & Compost Calculator
Filling a raised bed or border with the wrong amount of soil is an easy way to overspend or run short halfway through a job. Whether you're topping up with topsoil, compost, or a multi-purpose mix, getting the volume right first means you can compare buying loose bulk bags against standard 50L or 70L bags with confidence. Enter your bed or border dimensions below and we'll do the maths for you.
Enter your raised bed or border dimensions
We'll work out how much soil or compost you need, in litres, m³ and standard bags.
Enter a length, width and depth greater than zero to see how much soil you'll need.
Recommended products
A few well-reviewed options for composting and filling your beds.
£129.99
Pros
- Three-stage composting chambers
- Click-together assembly, no tools required
- Large 466L capacity suits big gardens
Cons
- Bulky — needs a dedicated corner
£219.00
Pros
- Rotating drum speeds up decomposition
- Elevated design deters pests and rodents
- No digging or turning by hand
Cons
- 190L capacity may be tight for larger households
£24.99
Pros
- Large 220L capacity at a low price
- Front hatch for easy compost access
- Lockable, air-tight lid
Cons
- Basic single-chamber design
- No aeration vents
Frequently asked questions
Topsoil or compost for a raised bed?
Most raised beds do best with a blend rather than one or the other: a good general mix is around 50-60% topsoil for structure and weight, combined with 40-50% compost or well-rotted manure for nutrients and drainage. Pure multi-purpose compost alone can hold too much water and settle quickly, while pure topsoil alone can be too dense and low in nutrients for vegetables.
How deep should soil be for vegetables?
Leafy crops and shallow-rooted veg like salad and herbs are fine with 15-20cm of soil, but most vegetables — beans, brassicas, courgettes — do better with 25-30cm. Root vegetables like carrots and parsnips need at least 30-40cm of loose, stone-free soil to grow straight and to size.
What is the difference between topsoil, compost and multi-purpose compost?
Topsoil is the mineral-rich soil dug from the ground, used mainly to fill volume and provide structure. Compost (garden or soil improver) is decomposed organic matter added to boost fertility and improve drainage or moisture retention. Multi-purpose compost is a lighter, more nutrient-dense growing medium, often peat-free, designed for containers and seed starting rather than bulk-filling large beds.
Why does my finished bed need less soil than I expected?
Loose soil and compost settle and compact by around 10-20% once watered in, so it's worth buying slightly more than the raw calculated volume, or planning to top up after the first few waterings.