Raised Bed Soil Calculator & How Much Soil to Buy
Fills raised beds
Find how much soil to buy for your raised beds — the volume in m³ and litres, the number of bags, the weight, and how much topsoil, compost and aeration your mix needs.
Enter your bed
Aeration = coco coir, perlite or coarse sand. Mix percentages are normalised, so they needn't add to exactly 100.
Next: buy ~10% extra for settling, mix the components before filling, and top up with compost each season as the level drops.
Volume = bed footprint × fill height; weight uses a blended bulk density. Mix percentages are normalised.
Raised-bed soil — key facts
- Volume
- L × W × H
- Min depth
- 20 cm (greens)
- Veg depth
- 30 cm
- Deep-root depth
- 40–45 cm
- Good mix
- 50/30/20 soil/compost/aeration
- Fill to
- ≈ 95% (below rim)
- 1 m³
- = 1000 L = 35.3 ft³
- Privacy
- Runs in your browser; nothing uploaded
Fill the bed right the first time
A raised bed is only as good as what you fill it with. Get the volume right and you avoid the classic mistakes — ordering one bag at a time at retail prices, or running short halfway through filling. The volume is just length × width × height, but the useful answer is the breakdown: how many bags, how much it weighs for delivery, and how much topsoil, compost and aeration to buy for a healthy mix.
This tool does all of that for one or several beds, with a fill level so you stop below the rim, and an optional cost. A balanced 50/30/20 mix of topsoil, compost and aeration suits most vegetables; go deeper (40 cm) for root crops or beds on paving. Buy ~10% extra for settling and top up with compost each season. Pair with the Mulch and Compost & Manure tools to finish the beds.
Order in bulk
Get the m³ figure bulk suppliers use — far cheaper than bags.
Get the mix right
See exactly how much topsoil, compost and aeration to buy.
Plan delivery
Know the weight before a tonne of soil lands on your driveway.
Scale to many beds
Calculate one bed or a whole plot of identical beds at once.
Frequently Asked Questions
How much soil do I need for a raised bed?+
Multiply length × width × height. A 2.4 × 1.2 m bed filled 30 cm deep needs about 0.86 m³ (860 litres) of soil. This tool calculates it for one or several beds, accounts for a fill level (usually ~95%), and converts to bags, litres and weight.
What is the best soil mix for a raised bed?+
A common, reliable blend is about 50% topsoil, 30% compost and 20% aeration (coco coir, perlite or coarse sand). The classic 'Mel's Mix' is one-third each of compost, peat/coir and vermiculite. The tool splits your total volume into each component so you know how much to buy.
How deep should a raised bed be?+
At least 20 cm for shallow-rooted greens and herbs, 30 cm for most vegetables, and 40–45 cm for deep-rooted crops like carrots, tomatoes and potatoes — or if the bed sits on a hard or paved surface. Deeper beds need proportionally more soil; the tool scales with your height.
How many bags of soil is that?+
Bagged soil is usually sold in litres (commonly 40 L). The tool divides your total volume by the bag size to give the bag count. Buying in bulk (by the cubic metre) is far cheaper for big or multiple beds — the m³ figure is what bulk suppliers use.
Why mix compost with topsoil?+
Pure topsoil compacts and is low in nutrients; pure compost is too rich and drains too fast. Blending gives structure, fertility, moisture retention and drainage together. The aeration component (perlite/coir/sand) keeps the mix from compacting so roots get oxygen.
How much will the soil weigh?+
A topsoil-based raised-bed mix weighs roughly 800–1100 kg per m³ depending on the blend and moisture — so a single 0.86 m³ bed is around three-quarters of a tonne. The tool estimates the weight from a blended bulk density so you can plan delivery and handling.
Should I fill the bed completely?+
Fill to about 2–5 cm below the rim so water and mulch don't spill over — that's why the tool defaults to a ~95% fill level. The soil will also settle after the first few waterings, so keep some spare mix to top up.
Can I save money on filling a deep bed?+
Yes — for very deep beds you can 'hügelkultur' the bottom third with logs, branches and coarse organic matter, then fill the top with your soil mix. Set the height to just the soil-mix layer in the tool. The woody base breaks down slowly and feeds the bed over years.
How do I convert m³ to cubic feet?+
1 m³ = 35.3 cubic feet ≈ 1.31 cubic yards, and 1 m³ = 1000 litres. The tool reports m³ and litres; multiply m³ by 35.3 if your supplier sells soil by the cubic foot.
Do I need to refill every year?+
Not fully — but raised-bed soil drops as organic matter breaks down, so top up with 3–5 cm of compost each season. That replaces lost volume and renews fertility. Re-run the tool with the top-up depth as the height to size the compost you need.