Measure the inside of the bed
Use the inside length and width, between the boards, and the depth you’ll actually fill. That’s often a little below the top of the walls. The calculator works out the volume:
Length × width × fill depth (in feet) = cubic feet. Divide by 27 for cubic yards, or by the bag size for bags.
A 4 × 8 foot bed filled 12 inches deep holds 32 cubic feet: 16 bags of 2 cubic feet, 11 bags of 3 cubic feet, or about 1.2 cubic yards in bulk.
Common bed sizes
| Inside size | Fill depth | Cubic feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|---|
| 4 × 4 ft | 12 in | 16 | 0.59 | 8 |
| 3 × 6 ft | 12 in | 18 | 0.67 | 9 |
| 4 × 8 ft | 6 in | 16 | 0.59 | 8 |
| 4 × 8 ft | 10 in | 26.7 | 0.99 | 14 |
| 4 × 8 ft | 12 in | 32 | 1.19 | 16 |
| 4 × 8 ft | 18 in | 48 | 1.78 | 24 |
For several beds the same size, set Number of areas instead of adding them up by hand.
How deep to fill depends on what you grow. University of Maryland Extension suggests at least 8 inches for leafy greens, beans and cucumbers, and 12 to 24 inches for peppers, tomatoes and squash when a bed sits on a hard surface.
Splitting soil and compost
If you’re mixing your own fill, enter the share that will be compost under Compost in the mix. The calculator splits the total and rounds each part up to whole bags, so you may end up with a little more than the total.
Oregon State Extension advises against filling raised beds with compost alone. For new raised beds it suggests adding 2 to 3 inches of compost or soil mix to the original soil, and when you reuse soil dug from the site, mixing in up to 25% compost by volume. Ask your supplier what their raised bed mix contains before adding more compost to it.
Before you order
Bag volumes are printed on the bag, in cubic feet or litres. Bulk suppliers sell by the cubic yard or cubic meter and set their own increments and minimums. Soil settles after watering, so you may want a few percent extra, or a bag or two for topping up later.
Keep your plan
Print your current plan or choose Save as PDF in the browser’s print dialog. Your inputs stay in a device draft when browser storage is available. An optional free account lets you save and sync the project in My projects. Calculating and printing stay open to everyone.
Read the measurement guide for the meaning of these quantities and worked examples.