Use this guide to plan topsoil for a raised bed at 12 inches deep, using a soil mix rather than plain topsoil alone. For a different bed size, use the Topsoil Calculator as the tool for custom sizes.
Recommended raised bed soil setup
Choose a soil mix for a raised bed, for example about 60% topsoil and 40% compost, so the bed holds moisture but still drains. Fill to 12 inches, water well, and expect the level to settle a little in the first weeks.
How much topsoil for a raised bed at 12 inches deep
Volume in cubic yards = length (ft) × width (ft) × 1 ÷ 27. The “order” column adds a 10% allowance for settling.
| Raised bed size | Area | Base volume | Order with 10% allowance |
|---|---|---|---|
| 4 × 8 ft | 32 sq ft | 1.19 cubic yards | 1.30 cubic yards |
| 4 × 12 ft | 48 sq ft | 1.78 cubic yards | 1.96 cubic yards |
| 8 × 8 ft | 64 sq ft | 2.37 cubic yards | 2.61 cubic yards |
Worked example: a 4 × 10 ft raised bed
Area = 4 × 10 = 40 sq ft. Volume = 40 × 1 ÷ 27 = 1.48 cubic yards. With a 10% settling allowance: 1.48 × 1.10 = 1.63 cubic yards. Order about 1.63 cubic yards of soil mix for this bed, then top up after the first watering and settling.
Method note
Measure the inside of the raised bed frame, not the outside, and use the full 12-inch fill depth. If the bed sits on hard ground, the same volume still applies; the mix is what changes, not the arithmetic.
Raised bed topsoil questions
Why a soil mix, rather than plain topsoil?
Plain topsoil can compact and drain poorly in a contained bed. Compost lightens the mix, adds nutrients, and helps roots grow through the full 12 inches.
How deep should a raised bed be filled?
Twelve inches suits most vegetables and flowers. Deeper-rooted plants benefit from more depth, but the volume rises in direct proportion to depth.
Why does the soil level drop after filling?
Loose soil settles when watered and when roots grow through it. The 10% allowance covers most settling; top up the bed rather than overfilling it at first.
Should I line the bottom of a raised bed?
On soil, no liner is usually needed. On concrete or paving, use drainage holes and a coarse layer so water can escape from the bottom of the bed.
For custom bed sizes, use the Topsoil Calculator.