Cubic feet, cubic yards, and liters

Keep length and volume separate, convert a quote correctly, and check an 8-by-4-bed example from start to finish.

By Raised Bed Soil Planner editorial project
Published 2026-10-27 · Reviewed 2026-10-27

Length tells you how far. Volume tells you how much three-dimensional space a material occupies. A cubic foot is the space in a cube with sides of one foot. A cubic yard is a cube with sides of one yard. Since a yard has three feet, that larger cube contains 3 × 3 × 3 = 27 cubic feet.

Convert the depth before you multiply

A bed 8 feet long and 4 feet wide, filled 12 inches deep, has a depth of 1 foot. Its volume is:

8 ft × 4 ft × 1 ft = 32 ft³

Multiplying 8 × 4 × 12 without converting the inches would give 384, which is not the volume in cubic feet. You can use different input units in the planner because it converts each length before multiplying.

For a metric example, a 240-centimeter by 120-centimeter space filled 30 centimeters deep is 2.4 × 1.2 × 0.3 = 0.864 cubic meters, or 864 liters. This is a separate example; it is not an exact conversion of the 8-by-4-foot bed.

A small conversion reference

These values follow the international foot definition, 1 foot = 0.3048 meter. The planner keeps decimal precision during the calculation and shortens only the displayed result. An on-screen value such as 1.185 cubic yards should not be copied as a more precise measurement than your tape allowed.

From a space to a purchase

For the 32-cubic-foot bed, divide by 27 to get approximately 1.185185 cubic yards. A supplier selling only multiples of half a cubic yard would require an order of 1.5 cubic yards. That order occupies 40.5 cubic feet: 8.5 cubic feet more than the measured space.

Buying 2-cubic-foot bags instead gives 32 ÷ 2 = 16 bags exactly. With a 5% optional reserve, the target becomes 33.6 cubic feet, so the order rises to 17 bags, or 34 cubic feet. The 0.4 cubic foot purchase rounding is separate from the 1.6 cubic feet you intentionally reserved.

Why we do not convert bag weight to volume

A 40-pound label describes mass, not capacity. Moisture, composition, and packing change how much space a given weight of material occupies. A bag of dense mineral soil and a bag of a lighter growing medium can have the same weight and different volumes. Get a stated volume from the supplier rather than using a universal pounds-to-cubic-feet shortcut.

Our supported volume labels are cubic feet, cubic yards, liters, and cubic meters. A label saying only “gallons” needs clarification about the gallon definition and what quantity is being described before it can be entered reliably.

A useful final check

Write your final need in the unit the supplier uses. Then confirm the order increment separately. Unit conversion answers “how much space?”; the purchase rule answers “what can I actually order?” Keeping those steps separate makes the difference between 1.185 cubic yards needed and 1.5 cubic yards bought easy to explain.

Sources & scope

• NIST — Guide to the SI, Appendix B: Conversion Factors

Examples and measurement explanations are original to this project. Sources provide unit definitions or gardening context; they do not endorse this tool. These guides were prepared with AI assistance. Read our editorial policy.