How deep should a raised bed be?
Raised bed depth follows the root depth of what goes in it. The volume follows the depth, and filling a bed takes more soil than almost anyone expects.
| Material | Depth | In inches | Where the depth comes from |
|---|---|---|---|
| Garden soil | 300 to 450mm | 11.8 to 17.7 in | Penn State Extension: a popular size is 4 feet by 8 feet by one foot deep, which is deep enough for annual plant root systems. The RHS puts 30cm as deep enough for salad leaves and strawberries. |
| Topsoil | 300 to 450mm | 11.8 to 17.7 in | Penn State Extension: a popular size is 4 feet by 8 feet by one foot deep, which is deep enough for annual plant root systems. The RHS puts 30cm as deep enough for salad leaves and strawberries. |
| Compost | 50 to 75mm | 2 to 3 in | Penn State Extension: plan on adding about two to three inches on the top and mixing it in with topsoil. Compost is a proportion of the fill rather than the whole depth. |
Working out the quantity once you have the depth
Multiply the area by the depth for a volume, then by the material's bulk density for a weight. Each calculator below does it in the units that material is sold in, and each shows the density range its figure came from.
Materials without a published depth for this use
No supplier read for this site publishes a laid depth for wood chip on a raised bed, so none is stated here. Their calculators take whatever depth you enter.