Rectangular Prism Volume Calculator
A rectangular prism is a box: six rectangular faces with square corners. Enter its length, width and height — in any mix of units — to get the volume, the surface area and the longest diagonal that fits inside.
- Surface area
- 432 in²
- Space diagonal
- 15.62 in
- Base area (length × width)
- 96 in²
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Enter the length, width and height, each in its own unit.
- Choose the volume unit: cubic inches, cubic feet, liters or gallons.
- Use the diagonal to check whether a long item will fit corner to corner.
Worked examples
A 12 × 8 × 6 in box: 576 in³, which is 9.44 liters
- Volume
- 576 in³
- Surface area
- 432 in²
- Space diagonal
- 15.62 in
- Base area (length × width)
- 96 in²
A 2 × 3 × 6 m container: 36 m³
- Volume
- 36 m³
- Surface area
- 72 m²
- Space diagonal
- 7 m
Converting between cubic units
There are 1,728 cubic inches in a cubic foot (12 × 12 × 12) and 27 cubic feet in a cubic yard. Dividing cubic inches by 12 instead of 1,728 is a very common slip. A 12 × 8 × 6 inch box is 576 in³, which is exactly one third of a cubic foot.
Aquariums and containers
A US gallon is 231 cubic inches. A tank 24 × 12 × 16 inches is 4,608 in³, or just under 20 gallons — measured to the brim and from the inside.
Questions people ask
What is the volume of a box 12 by 8 by 6 inches?
12 × 8 × 6 = 576 cubic inches, or 0.33 cubic feet.
What is the difference between a rectangular prism and a cube?
A cube is a rectangular prism whose length, width and height are all equal.
How long an item fits in a box?
Up to the space diagonal. In a 12 × 8 × 6 inch box that is √244 = 15.62 inches, ignoring the item’s thickness.