Width: reach the middle
The main point of a raised bed is soil you never walk on. Iowa State University Extension's rule is that a bed you can reach from both sides can be 3–4 feet wide, 0.9–1.2 m, while one against a building or fence should be no wider than 1½–2 feet, 0.45–0.6 m, about an arm's reach. Wider beds tempt you to kneel or step on the soil, which compacts it.
Length: whatever fits
Iowa State leaves the length to space and convenience. In practice the materials often decide it. Timber sleepers come in 1.8, 2.4 and 3.0 m lengths, so a 2.4 m sleeper makes a 2.4 m side and, cut in half, two 1.2 m ends. The sleeper bed calculator shows how bed sizes that don't fit the stock lengths waste timber.
Height: how deep for what you grow
The raised bed depth guide has the detail. In short, 30 cm suits most vegetables and herbs on open soil, 40–45 cm suits root crops such as carrots and potatoes and deep-rooted tomatoes, and 45–60 cm is needed on concrete or paving, where roots can't go any deeper. Taller beds are easier on the back but cost more to fill.
Paths between beds
Iowa State suggests paths about 3 feet, 0.9 m, wide if a wheelbarrow or cart has to pass. Where you only walk and kneel, narrower paths are fine. Mulch or gravel on the paths keeps the weeds down; the mulch calculator and gravel calculator work out how much.
How much soil each size holds
Volume is simply length × width × depth, and 1 m³ is 1,000 litres. The table uses 30 L bags and 1.3 t per m³ for bulk garden soil, the middle of the usual 1.2–1.4 t range.
| Bed (inside) | Area | 30 cm deep | 40 cm deep | 60 cm deep |
|---|---|---|---|---|
| 1.2 × 1.2 m | 1.44 m² | 432 L · 15 bags | 576 L · 20 bags | 864 L · 29 bags |
| 1.8 × 0.9 m | 1.62 m² | 486 L · 17 bags | 648 L · 22 bags | 972 L · 33 bags |
| 2.4 × 0.9 m | 2.16 m² | 648 L · 22 bags | 864 L · 29 bags | 1,296 L · 44 bags |
| 2.4 × 1.2 m | 2.88 m² | 864 L · 29 bags | 1,152 L · 39 bags | 1,728 L · 58 bags |
| 3.0 × 1.2 m | 3.60 m² | 1,080 L · 36 bags | 1,440 L · 48 bags | 2,160 L · 72 bags |
| 1.2 m round | 1.13 m² | 339 L · 12 bags | 452 L · 16 bags | 679 L · 23 bags |
Bags are 30 L, rounded up. Measure the inside of the bed, not the outside: 50 mm thick sleepers take 10 cm off each dimension. A round bed's area is π × radius², so a 1.2 m circle is 3.14 × 0.6 × 0.6 = 1.13 m². Allow 10–15 % extra for settling in the first year.
Bags or bulk?
At 1.3 t per m³, a 2.4 × 1.2 m bed 40 cm deep holds about 1.5 t of soil, far more than a car or a small trailer should carry in one trip. Somewhere between 0.5 and 1 m³, bulk delivery becomes cheaper than bags; the bagged vs bulk guide works through the break-even point. To save soil in a deep bed, fill the bottom with cheaper layers, as the guide to filling a bed cheaply explains.
Questions
What is the best size for a raised garden bed?
For a bed you can walk around, 1.2 m wide and as long as suits the space, often 2.4 m because that is a common sleeper length. Make it 30 cm deep for most vegetables and 40–45 cm for root crops. Against a fence, keep it to 0.45–0.6 m wide.
How much soil do I need for a 2.4 × 1.2 m raised bed?
864 litres at 30 cm deep, 1,152 L at 40 cm and 1,728 L at 60 cm, measured inside the bed. At 40 cm that is 39 bags of 30 L or about 1.2 m³ of bulk soil, plus 10–15 % for settling.
How wide should the paths between raised beds be?
About 0.9 m if a wheelbarrow or cart has to pass, according to Iowa State University Extension. Paths you only walk along can be narrower.
How tall should a raised bed be?
About 30 cm for most vegetables on open ground, 40–45 cm for root crops and tomatoes, and 45–60 cm on concrete or paving. Higher beds are easier to reach but hold much more soil.
Sources and method
- Iowa State University Extension, How do I construct a raised bed? What is a good size for a raised bed planter? – widths for two-sided and one-sided access, length, paths.
- Volumes: length × width × depth, 1 m³ = 1,000 L; round beds π × r² × depth. Bags rounded up to whole 30 L bags.
- Soil weight 1.2–1.4 t/m³ and settling of 10–15 %: see the bags per cubic metre guide and the raised bed soil guide.
- Sleeper lengths of 1.8, 2.4 and 3.0 m: as on the sleeper bed calculator.
Last reviewed 23 September 2026 · Report an error