Quick answer
Multiply the inside length by inside width by the intended soil depth in feet. Convert cubic feet to cubic yards by dividing by 27, or divide by the bag volume for bag estimates.
Step by step
- Measure inside dimensions. Use the actual fill area, not the outside frame size.
- Choose fill depth. Account for the finished soil level.
- Calculate cubic feet. Multiply length × width × depth.
- Convert quantity. Use cubic yards or the exact bag volume.
Formula or rule of thumb
soil volume = length × width × depth
Example
A 4 ft × 8 ft bed filled 1 ft deep needs 32 ft³, or about 1.19 yd³.
Common mistakes
Do not divide by 27 when you need bags unless you also use the bag's printed cubic-foot volume.
Planning note: product yields, installation methods, site conditions and local requirements can change the final quantity. Use the exact manufacturer or supplier information before purchasing.
FAQ
Should I include settling?
Bulk soil can settle, so ask the supplier how delivered volume is represented.
Can beds have different depths?
Split the bed into sections and calculate each depth separately.
How do I calculate bags?
Divide total cubic feet by the cubic feet per bag and round up.