Volume calculator
The volume of a box, cylinder, sphere or cone, in litres, cubic metres and gallons at once.
Measure across, not from the middle
Every volume formula for a round shape is written with the radius, the distance from the centre to the edge. Nobody can find the centre of a water butt to measure from, but anybody can put a tape across it. So this page asks for the diameter, the full width, and the working line halves it where you can see it happen.
Getting that wrong is not a small error. Put a diameter into a formula that wants a radius and the answer comes out four times too big for a cylinder or a cone, and eight times for a sphere.
Inside, not outside
For what a tank holds, measure its inside. Walls cost more capacity than they look like they should: 2 cm of wall on a tank 60 cm across leaves 56 cm inside, and that takes about 13% off what it holds. Measure the height to the overflow rather than the rim, because nothing is ever filled past it.
The units things are sold in
The answer comes in all of them at once because different things are bought in different units. Water butts and fuel tanks are sold in litres. Concrete, topsoil and gravel by the cubic metre. Skips are still hired by the cubic yard, which is why an "8-yard skip" holds 6.1 m³. Hot tubs and aquariums designed in America quote US gallons, which are about a sixth smaller than UK gallons, so the same tub can look a sixth bigger on a US spec sheet.
Pouring a slab? The concrete calculator takes the same measurements and says what to order.
Common questions
- How many litres are in a cubic metre?
- A thousand. A litre is a cube 10 cm along each side, and ten of those fit along each edge of a metre cube, so 10 × 10 × 10 of them fill it. That is why a 1,000-litre water tank is a cubic metre.
- How big is an 8-yard skip?
- Eight cubic yards, which is 6.1 cubic metres. Skips are still named by the cubic yard, so the "yard" in a skip size is a volume, not a length. A 6-yard skip is 4.6 m³ and a 12-yard one 9.2 m³.
- Should I measure a tank inside or outside?
- Inside, for what it holds. The walls take up room, and more than people expect on a round tank: 2 cm of wall on a 60 cm tank takes about 13% off the capacity. And measure the height only to the overflow, since a tank is never filled past it.
- Why are UK and US gallons different?
- They were defined separately. A UK gallon is 4.546 litres and a US gallon 3.785, so a US gallon is about a sixth smaller. Hot tubs, aquariums and pool equipment designed in America are usually rated in US gallons even when sold here.
- How do I work out the volume of an odd shape?
- Split it into shapes this page knows, work each out, and add them. A pond with a shallow shelf is two boxes. A skip-shaped heap is close to a pyramid. For anything curved and irregular, the average depth times the surface area is usually near enough.