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Topsoil calculator
Put your bed size, depth and bag size in: a 10 ft by 4 ft bed, 6 in deep, needs 20 cu ft of topsoil — 0.74 cubic yards, or 10 bags at 2 cu ft each.
★ CONSTRUCTION · GARDEN · TOPSOIL
Topsoil Calculator: 10 Bags for a 10×4 ft Garden Bed
On the defaults — a 10 ft by 4 ft bed, 6 in deep, 2 cu ft bags — you need 10 bags of topsoil, or 0.74 cubic yards. This is the topsoil tool: measure the bed once, and fill it once, with the depth checked after the first watering.
What does topsoil needed 10 bags mean?
It means ten bags of soil, at 2 cubic feet a bag, fill a 10 ft by 4 ft bed to a depth of 6 in. The volume is the whole story: 10 times 4 times half a foot of depth is 20 cubic feet, and 20 divided by 2 is exactly 10 bags — no rounding, no spare, which is rare enough to be worth noting. In cubic yards, the bulk-delivery unit, that is 20 divided by 27, or 0.74 yards: under a yard, so bags beat a bulk delivery for a bed this size, since most suppliers charge a delivery fee that dwarfs a sub-yard load.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Volume | length × width × depth ÷ 12 | 20 cu ft — 10 × 4 × 6 ÷ 12. |
| Cubic yards | volume ÷ 27 | 0.74 yards — 20 ÷ 27. |
| Bags | volume ÷ bag size, rounded up | 10 bags — 20 ÷ 2, exactly. |
Three things to check before you trust the number
First, check the bag size on the label: bags sold as 2 cu ft sometimes hold 1.5 cu ft after settling, and that alone would take this bed from 10 bags to 14. Second, decide whether the bed is being filled or topped up: a new bed needs the full 6 in, but a bed that already has soil only needs the top 2 in replaced, which is a third of the volume here. Third, remember the depth is the finished depth after watering and settling — soil settles by roughly a tenth, so fill a little proud and let the first watering take it down.
Worked example
10 ft long, 4 ft wide, 6 in deep, 2 cu ft bags. Volume: 10 × 4 × 6 ÷ 12 = 20 cu ft. Cubic yards: 20 ÷ 27 = 0.74. Bags: 20 ÷ 2 = 10 exactly. In practice that means ten bags, carried to the bed and tipped in, with no spare bag for the corners that settle first — buy an eleventh bag if the bed is new and the soil will be watered hard on day one. If the same bed were 12 in deep instead, the volume would be 40 cu ft and the need 20 bags, so depth alone would double the shop list.
Every branch, checked
With a 12 ft long bed instead of 10 ft, the volume rises to 24 cu ft and the need to 12 bags, or 0.89 cubic yards. With a 6 ft wide bed, the volume rises to 30 cu ft and the need to 15 bags, or 1.11 cubic yards. With a 12 in depth, the volume rises to 40 cu ft and the need to 20 bags, or 1.48 cubic yards. With 3 cu ft bags, the volume stays 20 cu ft but the need falls to 7 bags, since 20 ÷ 3 = 6.67 and bags round up. The bag count is a step function: volume moves smoothly, the shop list jumps only at whole bags.
The reverses, worked backwards
The length behind 10 bags is 10 ft: at 8 ft the need is 8 bags (16 cu ft, 0.59 cubic yards); at 12 ft it is 12 bags (24 cu ft, 0.89 cubic yards). The width behind 10 bags is 4 ft: at 3 ft the need is 8 bags (15 cu ft, 0.56 cubic yards); at 5 ft it is 13 bags (25 cu ft, 0.93 cubic yards). The depth behind 10 bags is 6 in: at 3 in the need is 5 bags (10 cu ft, 0.37 cubic yards); at 12 in it is 20 bags (40 cu ft, 1.48 cubic yards). Each reverse moves one input and holds the rest, so the step is exactly one dimension or one depth change.
What the defaults assume
The defaults assume a 10 ft by 4 ft rectangular bed, a flat 6 in soil layer, and bags of 2 cu ft. They do not assume existing soil underneath, settling after watering, a sloped bed, or compost mixed in — a bed filled over existing soil needs only the top-up depth, and compost replaces soil volume one-for-one.
Who uses this
- A gardener filling a new raised bed: the 10-bag buy settles the garden-centre trip before the first bag is tipped.
- A vegetable grower topping up beds in spring: the same maths on the top-up depth alone gives the spring order, not the full fill.
- A landscaper quoting a bed build: volume, yards, bags — the quote follows the same three steps, and the bag line shows the client why.
- A homeowner comparing bags against bulk: the 0.74-yard figure shows when a bulk delivery stops being worth its fee.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the bag size and the settling. Real bags vary in fill, soil settles by roughly a tenth after watering, and a bed is rarely a perfect rectangle — so treat 10 bags as the planning buy for a flat 6 in bed at honest 2 cu ft bags, and buy one spare for a new bed. If the supplier sells by the yard instead, the 0.74-yard figure is the number to quote.
Cite this calculator
Bright Side Kit, “Topsoil Calculator: 10 Bags for a 10×4 ft Garden Bed”, https://brightoolbox.com/topsoil-calculator/, accessed 2 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (10 ft × 4 ft bed, 6 in deep, 2 cu ft bags) so the 10-bag result can be checked.
Frequently asked questions
How many bags of topsoil do I need for a 10×4 bed?
10 bags at 2 cu ft each. The bed holds 20 cu ft at 6 in deep, and 20 ÷ 2 = 10 exactly.
How many cubic feet is a bag of topsoil?
Commonly 2 cu ft, which is the size this calculator uses. Check the label: some bags hold 1 or 1.5 cu ft, and a smaller bag raises the count for the same bed.
How deep should topsoil be in a raised bed?
About 6 in for vegetables, which is the depth this calculator uses. Flowers manage with 4 in; deep-rooted vegetables want 12 in, which doubles this bed to 20 bags.
Should I buy topsoil in bags or in bulk?
For under a cubic yard, bags: this bed is 0.74 yards, and a bulk delivery fee usually dwarfs a sub-yard load. For several beds totalling over 2 yards, bulk is cheaper per yard.
Does topsoil settle after watering?
Yes, by roughly a tenth. Fill a little proud of the finished depth and let the first watering take it down, or buy one spare bag for a new bed.
How do I price the topsoil once I know the bags?
Multiply bags by the per-bag price and add delivery if any. The sod calculator prices the lawn beside the bed on the same measure-then-order logic.