What volume measures
Volume is the amount of space a 3D object takes up, or how much it can hold. It is measured in cubic units, such as cubic inches, cubic feet or cubic meters, because you multiply three lengths together. For liquids, volume is often given in gallons or liters instead, and the calculator converts between them for you.
Volume formulas
| Shape | Formula |
|---|---|
| Cube | side³ |
| Box (rectangular prism) | length × width × height |
| Cylinder | π × radius² × height |
| Sphere | 4/3 × π × radius³ |
| Hemisphere | 2/3 × π × radius³ |
| Cone | 1/3 × π × radius² × height |
| Pyramid | 1/3 × base length × base width × height |
Worked examples
How many gallons does a fish tank hold?
A tank measures 30 × 12 × 12 inches. Its volume is 30 × 12 × 12 = 4,320 cubic inches. A US gallon is 231 cubic inches, so the tank holds 4,320 ÷ 231 ≈ 18.7 gallons. In practice you will fill it a little less because of gravel, decorations and the gap at the top.
How much water fits in a round tank?
A cylindrical tank is 4 feet across and 5 feet tall. The radius is 2 feet, so the volume is π × 2² × 5 ≈ 62.83 cubic feet. At 7.48 gallons per cubic foot, it holds about 470 gallons.
Tips for accurate measurements
- Measure the inside of a container if you want to know how much it holds, and the outside if you want to know how much space it takes up.
- Use the same unit for every measurement of a shape.
- For a round object, measure across the widest point to get the diameter, then halve it for the radius.
- For odd shapes, split them into simple parts, such as a box and a half cylinder, and add the volumes.
Filling a garden bed or pouring a slab? The cubic yard calculator works in the units suppliers sell by.
Last reviewed October 2026.