Raised garden bed soil calculator: how to fill it
Fill volume = inner length × inner width × fill height. A Brick Premium bed 70¾ × 35½ in with a height of 21¼ in holds 25 cu ft right to the rim (0.9 cu yd).
- 25 cu ft
- fill for a 70¾ × 35½ in bed to the rim
- 2⅜ in
- wall thickness you subtract twice
- 27
- cubic feet make one cubic yard
Updated 10/21/2026
Why count the inner size
The bed's walls are 2⅜ in thick. So you subtract the wall thickness twice from both the outer length and width. Long beds have a divider in the middle that reduces the volume a bit further.
Fill volume for common sizes
| Bed size | Per 4 in | Height 11¾ in | Height 16½ in | Height 21¼ in |
|---|---|---|---|---|
| 47¼ × 23½ in | 2 cu ft | 5 cu ft | 8 cu ft | 10 cu ft |
| 47¼ × 35½ in | 3 cu ft | 9 cu ft | 12 cu ft | 16 cu ft |
| 47¼ × 47¼ in | 4 cu ft | 12 cu ft | 17 cu ft | 22 cu ft |
| 70¾ × 23½ in | 3 cu ft | 9 cu ft | 12 cu ft | 15 cu ft |
| 70¾ × 35½ in | 5 cu ft | 14 cu ft | 19 cu ft | 25 cu ft |
| 70¾ × 47¼ in | 6 cu ft | 19 cu ft | 27 cu ft | 35 cu ft |
| 94½ × 23½ in | 4 cu ft | 12 cu ft | 16 cu ft | 21 cu ft |
| 94½ × 35½ in | 6 cu ft | 19 cu ft | 26 cu ft | 34 cu ft |
| 94½ × 47¼ in | 9 cu ft | 26 cu ft | 37 cu ft | 47 cu ft |
| 118 × 23½ in | 5 cu ft | 15 cu ft | 21 cu ft | 26 cu ft |
| 118 × 35½ in | 8 cu ft | 24 cu ft | 33 cu ft | 43 cu ft |
| 118 × 47¼ in | 11 cu ft | 33 cu ft | 46 cu ft | 59 cu ft |
How to fill a raised garden bed by layer
A layered fill saves soil and the bottom layers gradually turn into nutrients. Order from the bottom:
- Coarse material: branches, wood chips. Holds its shape and water drains through it easily.
- Grass and leaves: turf turned roots-up, mown grass, leaves.
- Compost: partly rotted or finished, feeds plants for a few more seasons.
- Topsoil: good garden soil or compost the plants can root into.
Choose the layer thickness based on what you have in your garden. The calculator works out the liters for each layer.
The fill will settle
A layered fill settles in the first season as the coarse material breaks down. Keep some soil back to top it up. We don't sell soil or compost: buy it at a garden center or builders' merchant, bagged or loose by the m³.
Frequently asked questions
How much soil does a raised garden bed need?
Multiply the inner length, width and fill height. A 70¾ × 35½ in bed with a height of 21¼ in holds 25 cu ft to the rim.
Do I have to fill the bed right to the rim?
No. Leave a few centimeters below the rim so water doesn't overflow when you water it. You set that in the calculator.
What should go on the bottom of a raised garden bed?
Coarse material like branches and chips. If you get voles in the garden, lay mesh on the bottom before the first layer.
How many bags of soil should I buy?
Divide the volume by the bag size on the packaging and round up. The calculator does it for you.