Volume is the amount of three-dimensional space a solid occupies, and it is the number that drives everything from ordering concrete for a driveway to sizing a fish tank, a shipping box, or a storage unit. This volume calculator handles the four most common 3D shapes people actually measure — the cube, the cylinder, the sphere, and the rectangular prism — and instantly converts your result into cubic feet, cubic yards, and US gallons.
Type a dimension and the result card updates on the spot. Because real-world materials are almost never sold in the same unit you measured in, the built-in conversions save you from the most common ordering mistake: guessing how much concrete, mulch, water, or soil you actually need.
How to Use
- Pick the Shape that matches your object. Most boxes, rooms, and packages are rectangular prisms; tanks, pipes, and barrels are cylinders; balls and round tanks are spheres; and a perfectly equal-sided box is a cube.
- Enter the Length / Side. For a cube this is the edge length; for a rectangular prism it is the longest dimension of the base. Cylinders and spheres ignore this field.
- Fill in Width and Height for a rectangular prism. Height is also used as the cylinder height — the distance between the two circular ends.
- Enter the Radius for a sphere or a cylinder. The radius is half the diameter, so if you measured across the middle of a round tank, divide that number by two first.
- Read the result in cubic feet, then check cubic yards and US gallons — the units you will actually use when you buy material or fill a container.
A zero dimension produces a volume of zero, which is correct: a flat box has no volume. Negative dimensions are rejected, because a negative length has no physical meaning.
The Volume Formulas
Every result comes from a standard solid-geometry formula taught in middle-school math and used by engineers, builders, and packagers worldwide:
- Cube: V = side × side × side
- Cylinder: V = π × radius² × height
- Sphere: V = (4/3) × π × radius³
- Rectangular prism: V = length × width × height
Here π (pi) is the constant 3.14159…, the ratio of any circle's circumference to its diameter. For a rectangular prism measuring 10 ft × 6 ft × 8 ft, the volume is simply 10 × 6 × 8 = 480 cubic feet, which converts to about 17.78 cubic yards or 3,591 US gallons. Notice how much larger the gallon figure is — a single cubic foot holds nearly 7.5 gallons of water, which is why even a small tank can weigh hundreds of pounds when full.
Cubic Feet, Yards, and Gallons: Why the Conversions Matter
Builders order concrete by the cubic yard, and a typical driveway pour runs around $120 per cubic yard delivered. A garden supply center sells mulch and topsoil by the cubic yard too, while aquarium and pond supplies are quoted in gallons. One cubic yard equals exactly 27 cubic feet, and one cubic foot equals about 7.48 US gallons.
That conversion is where people lose money. A homeowner who measures a flower bed as "10 by 6 by 1 foot" and orders by the square footage will buy far too little; the bed holds 60 cubic feet, which is about 2.22 cubic yards of mulch. Run the dimensions through this calculator before you call the supplier, and the quoted cubic-yard figure is the one you pay for.
Shape-Specific Tips
For a cylinder, measure the diameter across the center and divide by two to get the radius, then measure the height from bottom to top. A cylindrical rain barrel with a 3 ft radius and 4 ft tall holds π × 9 × 4 ≈ 113 cubic feet, or roughly 846 gallons — the reason two rain barrels can supply a whole garden.
For a sphere, the volume grows with the cube of the radius. Doubling a sphere's radius makes it eight times larger, not twice as large. A 5 ft radius sphere holds about 523.6 cubic feet (roughly 3,917 gallons), which is useful for sizing a round stock tank or a spherical water feature.
For a rectangular prism, measure inside the walls, not the outside, if you are calculating capacity. The difference between inner and outer dimensions is only a few inches, but on a large storage room those inches add up to a full extra yard of material.
Examples
Example 1 — Concrete driveway. A driveway 20 ft long, 10 ft wide, and 0.5 ft thick is a rectangular prism: 20 × 10 × 0.5 = 100 cubic feet, or about 3.70 cubic yards. At roughly $120 per cubic yard, the concrete alone costs about $445 before delivery and labor — far cheaper than ordering a generic "truckload."
Example 2 — Cylindrical water tank. A tank with a 2 ft radius and 6 ft height holds π × 4 × 6 ≈ 75.4 cubic feet, or about 564 gallons. This tells you the weight of a full tank: 564 gallons of water weighs nearly 4,700 lb, so the floor must be engineered for it.
Example 3 — Shipping cube. A cube-shaped crate with 4 ft edges holds 4 × 4 × 4 = 64 cubic feet, about 2.37 cubic yards. Knowing the cubic volume prevents you from being charged by the pallet for empty space you did not need.
FAQ
How do I calculate the volume of a cylinder?
Use the formula V = π × radius² × height. Measure the diameter across the center of the circular end, divide by two to get the radius, then measure the height between the two ends. Multiply π (about 3.14159) by the radius squared, then by the height. This calculator does it for you when you choose the cylinder shape.
What is the formula for the volume of a sphere?
The volume of a sphere is V = (4/3) × π × radius³. Cube the radius first, multiply by π, then multiply by four-thirds. Because the radius is cubed, a sphere grows eight times larger when its radius doubles.
How do I convert cubic feet to cubic yards?
Divide the cubic-foot figure by 27. There are exactly 3 feet in a yard, so a cubic yard is 3 × 3 × 3 = 27 cubic feet. For example, 480 cubic feet equals 480 ÷ 27 ≈ 17.78 cubic yards, which is the figure concrete and mulch suppliers use.
How many gallons are in a cubic foot?
One cubic foot holds about 7.48 US liquid gallons. Multiply your cubic-foot volume by 7.48052 to convert. A 64-cubic-foot cube therefore holds roughly 479 gallons, which is useful for sizing aquariums, ponds, and rain barrels.
What is the volume of a rectangular prism?
Multiply length × width × height. For a box, room, or flower bed, simply measure the three inside dimensions and multiply them together. If any dimension is zero, the volume is zero, because the shape has no depth.
Why should I measure inside dimensions for capacity?
When you are calculating how much a container can hold, measure the inner dimensions, because the walls, floor, and lid themselves take up space. The difference is small on a small box but becomes significant on a large storage room or tank, where measuring the outside could lead you to over-order material or overestimate capacity.
Disclaimer
This volume calculator is provided for informational purposes only and does not constitute engineering, construction, or commercial advice. Volume figures are based on the dimensions you enter and the standard solid-geometry formulas; real objects may be irregular, hollow, or measured imprecisely. Always confirm material quantities and structural capacity with a qualified supplier or contractor before ordering concrete, soil, or designing load-bearing installations.