How to use it
- Pick a solid shape.
- Choose the unit of your measurements.
- Enter the dimensions.
- Read the volume in cubic units, gallons, liters and cubic feet.
Volume formulas
| Shape | Volume |
|---|---|
| Cube | V = a³ |
| Rectangular box | V = l × w × h |
| Cylinder | V = πr²h |
| Sphere | V = 4/3 × πr³ |
| Cone | V = πr²h / 3 |
| Square pyramid | V = a²h / 3 |
| Frustum (bucket) | V = πh / 3 × (R² + Rr + r²) |
| Triangular prism | V = (√3/4) × a² × h |
Pick a shape and unit, enter the dimensions, and the calculator shows the volume in cubic units plus US gallons, liters, cubic feet and cubic meters. It also shows the surface area. Everything is calculated in your browser.
Worked examples
- Aquarium: 30 × 12 × 18 inches = 6,480 cubic inches. Divide by 231 cubic inches per gallon: about 28.05 gallons.
- Water tank: a cylinder 3 ft across (radius 1.5 ft) and 4 ft tall: π × 1.5² × 4 ≈ 28.27 cu ft, or about 211.5 gallons.
- Ball: a sphere with a 6-inch radius: 4/3 × π × 216 ≈ 904.8 cu in, about 3.92 gallons.
- Mulch bed: 10 ft × 10 ft × 4 in deep (1/3 ft) = 33.3 cu ft ≈ 1.23 cubic yards.
Volume unit conversions
| Unit | Equals |
|---|---|
| 1 cu ft | 1,728 cu in ≈ 7.48 US gallons |
| 1 cu yd | 27 cu ft |
| 1 US gallon | 231 cu in ≈ 3.785 liters |
| 1 liter | 1,000 cm³ ≈ 0.264 US gallons |
| 1 m³ | 1,000 liters ≈ 35.31 cu ft |
US gallons and UK (imperial) gallons differ: an imperial gallon is about 4.546 liters. This calculator uses US gallons.
Buckets and tapered containers
A bucket, planter or flowerpot that is wider at the top is a frustum, a cone with the tip cut off. Measure the radius at the bottom (R) and top (r) and the height. A 5-gallon bucket, for example, is roughly 10.4 inches across at the bottom and 12 inches at the top; the calculator gives the exact volume for your own measurements.
For a cone-shaped pile of gravel or sand, measure the diameter at the base and the height, then use the cone.
Tips for accurate results
- Use inside dimensions for containers. Wall thickness can make a big difference in small tanks.
- Keep units consistent. Convert everything to inches or everything to feet before entering, or the result will be wrong by a large factor.
- Real capacity is lower. Aquariums are rarely filled to the brim, and gravel and decorations take space.
- Concrete and landscaping: for slabs, footings and posts, use the concrete calculator, which works in cubic yards and bags.
For the outside area of a shape, see the surface area calculator.
Common mistakes
- Using the diameter as the radius. A 3-foot-wide tank has a 1.5-foot radius; using 3 makes the volume four times too big.
- Mixing inches and feet. A slab 10 ft by 10 ft by 4 in is not 400 cu ft; convert 4 inches to 1/3 ft first.
- Forgetting the 1/3 in cone and pyramid formulas. A cone holds exactly one third of a cylinder with the same base and height, and a sphere two thirds of the cylinder that fits around it.
- Confusing volume with surface area. Volume is in cubic units; surface area is in square units.
Frequently asked questions
How do I calculate volume in gallons?
Find the volume in cubic inches and divide by 231, or in cubic feet and multiply by 7.48. The calculator does this automatically.
What is the volume of a cylinder?
V = πr²h. A cylinder with a 1.5 ft radius and 4 ft height holds about 28.27 cubic feet, or 211.5 gallons.
How many cubic feet are in a cubic yard?
27 cubic feet (3 × 3 × 3).
How do I find the volume of a bucket?
Choose the frustum shape and enter the bottom radius, top radius and height.
Does it use US or imperial gallons?
US gallons (231 cubic inches, about 3.785 liters).
Last updated: November 12, 2026