Settling is driven by organic content.
Area 1
For a tree ring. 0 if solid.
Measure it. Do not assume.
Leave 1 in below the rim.
Advanced options
0 = use the figure for your mix.
Per cubic metre if metric.
Topsoil 2,000–2,400 damp.
Only for beds over 18 in deep.
This soil calculator covers beds, borders and containers — and treats a tapered pot as the cone it actually is, rather than a cylinder, which is where most container estimates go 30% wrong.
The short answer
Soil volume is area × depth. A 4 × 8 ft bed at 12 in deep is 32 ft³ — about 1.0 m³, or 1,042 litres once you allow for settling.
Containers are different. A pot 12 in across the top, 9 in at the base and 11 in deep holds 15.7 litres, not the 20.4 the cylinder formula gives.
On this page
How to use this soil calculator
Pick a mix, then describe the space. Four modes:
- Rectangular bed — length, width and depth
- Round bed — diameter and depth, with an optional centre hole for tree rings
- Pots & planters — top diameter, base diameter and fill depth
- Known area — you’ve already worked out the square footage
The header toggle switches the headline figure between cubic yards and cubic metres. Litres are always shown, since that’s how bagged soil is labelled almost everywhere outside the US.
Add as many areas as you like — a bed, a border and a set of pots all in one order.
Why pots hold less than they look
Almost every flowerpot tapers. It has to, or you couldn’t stack them, and the plant couldn’t be tipped out. But that taper means a pot is a frustum — a cone with the top sliced off — and not a cylinder.
Measure the rim, apply πr²h, and you’ve assumed the base is as wide as the top. It isn’t, and the error compounds because volume goes with the square of the radius.
| Pot, 12 in top × 11 in deep | True volume | Cylinder says | Over by |
|---|---|---|---|
| 12 in base — no taper | 20.4 L | 20.4 L | 0% |
| 11 in base | 18.7 L | 20.4 L | 9% |
| 10 in base | 17.2 L | 20.4 L | 19% |
| 9 in base — typical | 15.7 L | 20.4 L | 30% |
| 8 in base | 14.3 L | 20.4 L | 42% |
| 6 in base — steep taper | 11.9 L | 20.4 L | 71% |
Six pots of the standard 12 / 9 / 11 in shape need 94 litres of mix. The cylinder formula says 122 — that’s four 25 L bags instead of five, and a fifth bag left over on a small job.
Scale it to a terrace full of planters and the difference is real money. Measure the base diameter. It takes five seconds and it’s the input nobody asks for.
The formula reduces exactly to πr²h when top and base are equal, so there’s no downside to using it — a straight-sided trough gives the same answer either way.
The formulas
Volume = Length × Width × Depth
Round bed = π × radius² × Depth
Tree ring = π × (R² − r²) × Depth
Depth in feet — divide inches by 12
Volume = π × h ÷ 3 × (R² + R×r + r²)
R = top radius · r = base radius · h = fill depth
When R = r this becomes π r² h — the cylinder
Worked example — 4 × 8 ft raised bed, 12 in deep, garden mix
How deep does soil need to be?
| Use | Depth | Metric |
|---|---|---|
| Lawn topdressing | ¼–½ in | 6–13 mm |
| New lawn or turf | 4–6 in | 100–150 mm |
| Flower beds | 6–8 in | 150–200 mm |
| Vegetable beds | 12–18 in | 300–450 mm |
| Shrubs | 18–24 in | 450–600 mm |
| Trees | 24–36 in | 600–900 mm |
Depth matters far more than area for whether things grow. Going deeper than the planting needs is money into the ground; going shallower limits roots in a way that’s very hard to fix once plants are established.
Lawn topdressing is the one people over-order on. A quarter inch across a whole lawn is a lot of soil in total, but any more than half an inch smothers the grass you’re trying to feed.
Settling depends on the mix
Soil drops after it’s watered in, and the amount is driven by how much organic matter it contains — organic material collapses as it wets and decomposes, while mineral soil barely moves.
| Mix | Settles | Order factor |
|---|---|---|
| Screened topsoil | 5% | × 1.05 |
| Fill dirt | 8% | × 1.09 |
| Garden mix 60/30/10 | 13% | × 1.15 |
| Potting mix | 20% | × 1.25 |
| Pure compost | 30% | × 1.43 |
Fill proud of the final level and water it in thoroughly before planting. Topping up later means working soil in around established roots, which is awkward and disturbs the plants you just put in.
Yards, metres and litres
Soil is one of the few materials sold in genuinely different units depending where you are, which is why this calculator gives all three.
| Unit | Equals |
|---|---|
| 1 cubic yard | 27 ft³ · 0.765 m³ · 765 L |
| 1 cubic metre | 1.308 yd³ · 35.31 ft³ · 1,000 L |
| 1 cubic foot | 28.32 L |
| 1 US gallon | 0.134 ft³ · 3.785 L |
The useful shortcut: a cubic metre is 1,000 litres exactly. If you’re buying 25 L bags, that’s 40 bags per cubic metre — which makes the bulk comparison very easy to do in your head.
Bags versus bulk
| Bag | Volume | Per yd³ | Per m³ |
|---|---|---|---|
| 40 lb topsoil | 0.75 ft³ · 21 L | 36 | 48 |
| 1 ft³ bag | 1 ft³ · 28 L | 27 | 36 |
| 2 ft³ bag | 2 ft³ · 57 L | 14 | 18 |
| 25 L bag | 0.88 ft³ | 31 | 40 |
| 50 L bag | 1.77 ft³ | 16 | 20 |
Bulk usually wins past about half a cubic yard, or roughly 12–15 bags. Below that the delivery charge dominates and bags are simpler.
Bags stay worth the premium when access is tight, when you need the job in stages, or when a bulk delivery would sit on a driveway you can’t block for a weekend. They’re also the only sane option for potting mix, which you want clean and consistent rather than shovelled off a pile.
Which soil for what
| Type | Use it for | Not for |
|---|---|---|
| Screened topsoil | Lawns, levelling, bulk filling of beds | Containers — too dense, drains badly |
| Garden mix | Raised beds, borders, general planting | Pots, unless heavily amended |
| Potting mix | Containers and pots exclusively | Beds — far too expensive per volume |
| Compost | Amending existing soil, topdressing | Planting into neat — too rich, holds water |
| Fill dirt | Levelling, raising grade, backfill | Anything you intend to grow in |
It seems like a saving and it kills plants. Garden soil compacts in a container without earthworms and weather to keep it open, and once compacted it holds water against the roots with nowhere to drain.
Potting mixes are built around bark, peat or coir precisely to stay open. They cost more per litre because they’re doing a different job.
Filling deep beds
A bed over 18 in deep doesn’t need soil all the way down, and filling it entirely is expensive. Logs, branches and coarse brush in the base cut the mix you buy, improve drainage, and break down over several years feeding the bed from below.
Two conditions. Keep at least 12 in of real soil above the fill — that’s what the roots use. And expect the bed to drop noticeably in its first two seasons as the wood collapses, so plan to top it up rather than being surprised.
On a 4 × 8 ft bed at 24 in deep, filling the bottom third saves about 600 litres of purchased mix.
Soil ordering mistakes to avoid
- Using the top diameter for a tapered pot. Overstates by 30% on a typical shape.
- Forgetting to allow for settling. Compost drops 30% and you can’t easily top up later.
- Putting garden soil in containers. It compacts and drowns the roots.
- Over-topdressing a lawn. More than half an inch smothers the grass.
- Ordering bags for a bulk job. Past 12–15 bags, bulk is usually cheaper.
- Confusing cubic yards with cubic metres. A metre is 31% more.
- Filling a deep bed entirely with soil. The bottom foot does no work.
- Skimping on depth for vegetables. 12 in is the practical minimum.
Frequently asked questions
How much soil do I need?
Multiply length × width × depth, with depth in feet. A 4 × 8 ft bed at 12 in deep is 32 ft³, which is 1.19 cubic yards or 0.91 cubic metres — about 1,042 litres once you allow for settling. Add the settling factor for your mix, since soil drops after watering.
How do I calculate soil for pots?
Not with the cylinder formula. A tapered pot is a frustum: π × height ÷ 3 × (R² + R×r + r²), where R is the top radius and r the base radius. A 12 in top, 9 in base, 11 in deep pot holds 15.7 litres — the cylinder formula says 20.4, which is 30% too much.
How deep should soil be for a vegetable garden?
12 to 18 inches of workable soil. Twelve is the practical minimum for most vegetables, and root crops like carrots and parsnips want the full 18. Flower beds manage on 6 to 8 inches, and a new lawn needs only 4 to 6 over a properly prepared base.
How much does soil settle?
It depends on organic content. Screened topsoil settles about 5%, a 60/30/10 garden mix around 13%, potting mix 20% and pure compost 30%. Fill proud of the final level and water in thoroughly before planting, rather than topping up around established roots later.
How many litres in a cubic metre of soil?
Exactly 1,000. That makes bag counts easy: 40 bags of 25 L, or 20 bags of 50 L, fill a cubic metre. A cubic yard is 765 litres, or about 31 bags of 25 L.
Is bulk soil cheaper than bags?
Usually, past about half a cubic yard or 12 to 15 bags. Below that the delivery charge dominates. Bags stay worth it when access is tight, you need the job in stages, or a bulk drop would block a driveway — and for potting mix, which you want clean rather than shovelled off a pile.
Can I use garden soil in pots?
No. Garden soil compacts in a container, because there are no earthworms or weather cycles to keep it open, and once compacted it holds water against the roots with nowhere to drain. Potting mixes are built around bark, peat or coir specifically to stay open.
What is the difference between topsoil and garden mix?
Topsoil is screened mineral soil — good for lawns, levelling and bulk filling, but low in organic matter. Garden mix blends topsoil with compost and an aeration material, typically 60/30/10, giving better structure and nutrition for planting. Garden mix costs more and settles more.
How much soil for a 4×8 raised bed?
At 12 inches deep, 32 ft³ before settling — about 1.36 cubic yards, 1.04 cubic metres or 1,042 litres of garden mix once the 13% settling allowance is added. That’s 19 bags of 2 ft³, or 42 bags of 25 L.
How much does a cubic yard of soil weigh?
Roughly 2,000 to 2,400 lb for damp screened topsoil, so about a ton per cubic yard. Compost is much lighter at around 1,100 lb, and saturated soil considerably heavier. That matters for what a pickup can legally carry — most half-ton trucks manage well under a full yard of wet topsoil.
Can I fill the bottom of a deep bed with something cheaper?
Yes, in beds over 18 inches deep. Logs, branches and coarse brush in the base cut the mix you buy and improve drainage, breaking down over several years to feed the bed. Keep at least 12 inches of real soil above the fill, and expect the bed to drop noticeably in its first two seasons.
Can I use this soil calculator in metric?
Yes — the header toggle switches the headline figure to cubic metres, and litres are always shown since that’s how bagged soil is labelled outside the US. Dimensions are entered in feet and inches; multiply feet by 0.3048 for metres.
Sources and method
- Container volume uses the frustum of a cone: π h ÷ 3 × (R² + Rr + r²), which reduces exactly to π r² h when the taper is zero
- Settling allowances scale with organic content, consistent with the approach used on our compost and raised bed calculators
- Conversions: 1 yd³ = 27 ft³ = 0.7646 m³; 1 m³ = 1,000 L = 35.31 ft³; 1 ft³ = 28.317 L
- Planting depths from general horticultural guidance; local conditions and specific crops vary
- Bag sizes differ by market and supplier — check the label, since 25 L and 1 ft³ bags are not the same volume
Related calculators
How this soil calculator works out its numbers
Beds and borders are area times depth, with depth converted from inches to feet. Round beds use π r², and a tree ring subtracts the inner circle so you aren’t buying soil for the space the trunk occupies.
Containers use the frustum formula rather than a cylinder, because a tapered pot genuinely holds less. The formula is exact, not an approximation — set the base diameter equal to the top and it returns πr²h to the decimal, so a straight-sided trough gives the same answer either way.
Settling is applied by dividing rather than multiplying: to finish with a given volume after a 20% drop you need volume ÷ 0.80, not volume × 1.20. That distinction is worth 5% on potting mix and more on compost. Bulk-fill for deep beds is deducted before settling is applied, since only the soil portion settles.
Settling figures are typical, not exact. How much a given mix drops depends on its actual organic fraction, how it was stored, and how thoroughly it’s watered in. Order a little over rather than under — a small surplus is useful for topping up in the second season, while running short means a second delivery charge for a fraction of a yard.