What this calculator does
It finds the space inside any box-shaped object: shipping cartons, rooms, raised garden beds, aquariums, storage bins or trench sections. Results are shown in several units so you can compare capacity (liters, gallons) and bulk materials (cubic feet, cubic yards).
Formula
V = l × w × h, where l, w and h are the length, width and height in the same unit. Converting cubic units cubes the linear factor: 1 ft³ = 12³ = 1,728 in³, and 1 yd³ = 3³ = 27 ft³.
Worked examples
Aquarium, 36 in × 18 in × 20 in
- 36 × 18 × 20 = 12,960 in³.
- 12,960 ÷ 231 (cubic inches per US gallon) ≈ 56.10 US gal.
- In liters: 12,960 × 0.016387064 ≈ 212.38 L.
Raised bed, 8 ft × 4 ft × 10 in
- Convert height: 10 in = 10 ÷ 12 ≈ 0.8333 ft.
- 8 × 4 × 0.8333 ≈ 26.67 ft³.
- 26.67 ÷ 27 ≈ 0.988 yd³ of soil.
Interpreting results
The result is the internal geometric volume. A tank's usable capacity is lower if it is not filled to the brim, and wall thickness matters if you measured outside dimensions. For bulk landscape materials with a waste allowance, use the cubic yards calculator; for concrete, the concrete calculator.
Common mistakes
- Measuring outside dimensions of a container with thick walls.
- Converting cubic feet to cubic yards by dividing by 3 instead of 27.
- Confusing US gallons (3.785 L) with Imperial gallons (4.546 L). This page reports US gallons.
Assumptions and references
All faces are assumed flat and square to each other. Unit definitions are exact: 1 in = 2.54 cm, 1 US gallon = 231 in³ = 3.785411784 L (NIST SP 811).
Frequently asked questions
What is a rectangular prism?
A solid with six rectangular faces where every corner is a right angle, such as a box, a brick, a room or a rectangular tank. A cube is the special case with all edges equal.
How many liters are in a cubic foot?
One cubic foot is exactly 28.316846592 liters, because 1 ft = 0.3048 m and a cubic meter holds 1,000 liters.
Can I mix units, such as feet and inches?
Yes. Each dimension has its own unit selector, and every value is converted to meters before multiplying.