Volume Calculator

Type in a shape's measurements and this tool gives you the volume instantly. The part that actually matters, and the part most volume calculators quietly skip: it converts that volume into liters and US gallons on every single result. Because "4,608 cubic inches" tells you nothing useful the moment you're filling a fish tank. Nobody buys water by the cubic inch. You want gallons, and you want them without running a second conversion by hand.

Pick a shape from the dropdown, fill in the boxes, and the answer updates as you type. No button to press, no sign-up, and nothing you enter ever leaves your browser. It covers the shapes you actually run into, cube, rectangular box, sphere, cylinder, cone, pyramid, and triangular prism, and it prints the exact formula it used right under the result so you can see where the number came from.

1. Pick your shape. The input boxes change to match it. A sphere asks for one radius, a box asks for length, width, and height, a triangular prism wants the triangle's base and height plus the length of the bar.
2. Set the unit (mm, cm, m, in, ft, yd). This is the label your answer reads out in, and it's what drives the liters and gallons conversion. It does not convert between units for you, so measure everything in the one unit you picked.
3. Enter the measurements. The volume shows up instantly below, with its capacity in liters and gallons on the line underneath.
4. Check the formula. The exact equation the tool applied sits under the number, handy for homework or for catching a mistyped dimension.
5. Change anything, the shape, a measurement, the unit, and it recalculates live.

Decimals are fine, type 2.5 for two and a half meters. A negative number gets a polite nudge instead of a nonsense answer, since a barrel can't be minus three feet tall.

A plain volume calculator stops at the cubic figure. You measure your tank at 24 by 12 by 16 inches, it says 4,608 cubic inches, and you're no closer to knowing anything useful. That figure won't tell you which heater to buy or how many fish the tank holds, and you still have to go dig up a cubic-inches-to-gallons converter and run the number a second time.

This tool does that step for you. That same tank reads out as roughly 75 liters, or about 20 US gallons, right there under the volume, and now the number actually means something. Twenty gallons sets your stocking limit, your heater wattage, and your water-treatment dose. The conversion is exact, one liter is 1,000 cubic centimeters and one cubic foot is about 7.48 US gallons, and the tool carries those factors so you don't have to.

For a tank, that figure runs high. The capacity you see is the geometric ceiling, filled to the very brim with nothing inside. A real aquarium holds noticeably less, because you leave an inch of headroom at the top and the gravel, rocks, and decorations all displace water. Treat the calculated gallons as the maximum and shade down from there. A stocked tank usually runs ten to fifteen percent under its raw geometric volume.

The same logic works for a rain barrel, a stockpot, a fermenter, a planter, a fuel can. Any time you need to know how much something holds, that gallons line gives it to you without a second conversion.

Most wrong answers trace back to one of two slips, and both are worth knowing before you trust any volume figure.

Radius, not diameter. The sphere, cylinder, and cone formulas all want the radius, the distance from the center to the edge, which is half the width across. Feed a sphere its diameter by mistake and the volume comes out eight times too big, because the radius gets cubed and doubling it multiplies by eight. A ball 6 inches across has a radius of 3. So if a sphere result looks wildly large, this is almost always why. Halve the number and re-enter it.

Mixing units. The tool multiplies your numbers exactly as typed. It has no idea that 2 feet and 24 inches are the same length. Enter one dimension in feet and another in inches and you get an answer that's off by a mile with nothing to warn you, because both numbers are perfectly valid on their own. Convert everything to a single unit first, set the dropdown to match, then read the result.

One more fact catches people out: volume scales with the cube of size. Double a tank's dimensions and it holds eight times as much water, not double. That's why a fish tank one size up needs dramatically more water than it looks like it should, and why scaling a recipe by "just a bit bigger" overshoots so hard.

The seven built-in shapes cover most of what real life hands you, but not everything is one clean solid. A grain silo is a cylinder with a cone on top. A capsule-shaped pill is a cylinder with a rounded half-sphere at each end. An L-shaped pool is two boxes.

The move is always the same. Break the object into simple pieces, calculate each one here, and add the numbers up. Silo: run the cylinder for the walls, run the cone for the roof, add the two. Capsule: one cylinder plus a full sphere, since the two rounded ends make one whole ball between them. Hollow things work the same way by subtraction. A pipe is a big cylinder with a smaller one bored out of the middle, so you find both and take the difference to get the volume of the wall itself, which is exactly what you'd cost a material order from.

For something genuinely irregular with no formula at all, a sculpture, an odd casting, there's the old water-displacement trick that never fails. Submerge it in a measuring jug and read how far the water rises, and that rise is the volume, no math needed.