Tank Volume Calculator
This tank volume calculator works out the capacity of a tank and how much liquid is in it right now. Pick a vertical cylinder, a horizontal cylinder, a rectangular tank, or a cone-bottom tank, type in the size, and add the dip depth if you want the filled volume. You'll get the total capacity and the amount inside in US gallons, Imperial gallons, and liters, with the formula shown. It's built for water tanks, fuel tanks, fish tanks, and more.
- 4 tank shapes
- Total and filled volume
- Dip depth and % full
- Gallons and liters
- Live liquid level
Last updated June 16, 2026 4 tank shapes, partial fill Reviewed by the Calcowa math team
Enter positive numbers to see the tank volume.
Show capacity in all units
V = π r² H
What is tank volume?
Tank volume, or tank capacity, is the amount of liquid a tank can hold when it's full. It's the inside space of the tank, measured in cubic units and then reported in the friendlier gallons or liters. A round tank uses the cylinder formula, a box tank multiplies its three sides, and a cone-bottom tank adds a cone to a cylinder. The shape decides the formula, but it's the same idea: how much fits inside.
Capacity is the full tank, while the filled volume is how much is in there at a given moment. That's why this tool asks for a dip depth: it tells you both numbers, so you'll know what you've got and how much room is left.
Tank volume formula by shape
Each tank shape has its own volume formula. Here are the four this calculator covers, where r is the radius, H or L is the height or length, and Hc and Hk are the cylinder and cone heights of a cone-bottom tank.
| Tank shape | Formula | Typical use |
|---|---|---|
| Vertical cylinder | V = π r² H | Upright round tank, like a water butt |
| Horizontal cylinder | V = π r² L | Tank lying on its side, like a fuel tank |
| Rectangular | V = L × W × H | Box or square tank, like a sump |
| Cone bottom | V = π r² Hc + ⅓ π r² Hk | Cylinder body with a cone underneath |
A round tank is really a cylinder, so the cylinder volume calculator shows the same math with hollow walls and pipes.
How do you calculate tank volume?
To calculate tank volume, match the tank to a shape, measure it, and apply the formula. Add a dip depth and you'll see how full it is. Here's the routine:
- 1
Pick the tank shapeUpright round, on-its-side round, box, or cone bottom.
- 2
Measure insideMeasure the inside diameter or sides, and the height or length.
- 3
Enter the dip depthType the liquid depth if you want the filled volume and percent full.
- 4
Read gallons or litersThe result gives the capacity and the amount inside in both.
Fill level and dip charts
A dip chart turns a stick reading into a volume, and it matters most for a tank lying on its side. A horizontal cylinder doesn't fill evenly: the same inch of depth holds far more liquid near the middle than near the top or bottom. The calculator handles this with the circular segment formula, so the filled volume you see matches what a proper dip chart would give. Set the fill depth above, and you'll get the gallons or liters at that level plus the percent full, which is handy for fuel tanks, oil tanks, and cisterns.
Tank volume in gallons and liters
Tanks get measured in cubic units, but nobody buys water by the cubic inch, so this tool converts for you. One US gallon is 231 cubic inches, one Imperial gallon is about 1.2 US gallons, and one liter is 1,000 cubic centimeters. Watch the gallon type: a UK or Canadian Imperial gallon is bigger than a US one, so you'll want the right one in the result. The liters figure sits right beside the gallons, so you don't have to convert anything yourself.
Water tanks, fuel tanks, and fish tanks
A water tank is usually an upright or horizontal cylinder, so pick that shape and read the liters or gallons. A fuel tank often lies on its side, and that's where the dip depth earns its keep. A fish tank or aquarium is a rectangular tank, so use the box shape, and keep in mind the water line sits a touch below the rim, so you won't quite fill it to the full capacity. Whatever you're filling, measure the inside, not the outside, so the walls don't sneak into your numbers.
Volume units and accuracy
Calcowa shows the capacity in US gallons, Imperial gallons, liters, cubic feet, and cubic meters at once. The round-tank math uses the full value of pi, so the result is accurate for plumbing, fuel, aquariums, and farm tanks alike.
| Unit | Best for | Good to know |
|---|---|---|
| US gallons (gal) | US tanks, pools | 1 US gal = 231 in³ |
| Imperial gallons | UK and Canada tanks | 1 imp gal = 1.201 US gal |
| Liters (L) | Most of the world | 1 L = 1,000 cm³ |
| Cubic feet (ft³) | Large water tanks | 1 ft³ = 7.48 US gal |
| Cubic meters (m³) | Industrial tanks | 1 m³ = 1,000 liters |
Frequently asked questions
Is tank volume the same as tank capacity?
Yes, the full tank volume is its capacity, the most it can hold. The filled volume is how much liquid is in it at a given dip depth, which is usually less than the capacity.
Match the tank to a shape, then apply its formula. A round upright tank is π r² H, a tank on its side is π r² L, and a box tank is length times width times height. The calculator above does all four shapes and converts the answer to gallons and liters for you.
Work out the volume in cubic units first, then convert: one liter is 1,000 cubic centimeters, and one cubic meter is 1,000 liters. This tool shows the capacity in liters right beside gallons, so you don't have to convert it by hand.
A tank on its side needs the circular segment formula, because the liquid surface is a chord across the circle. Enter the diameter, length, and the dip depth above, and the calculator works out the filled volume and the percent full, which is what a dip chart shows.
A dip chart turns the depth of liquid, measured with a dipstick, into a volume. Because a round tank doesn't fill evenly, the same inch of depth holds more near the middle than near the top or bottom. Set the fill depth above and you'll get the matching volume, which is one row of a dip chart.
Multiply length by width by height for the full capacity, all in the same unit. A tank 4 by 2 by 3 feet holds 24 cubic feet, which is about 180 US gallons. Pick Rectangular above and read the gallons and liters from the result.
Measure the inside length, width, and height, multiply them, and the calculator converts to gallons. A tank 24 by 12 by 16 inches holds about 20 US gallons. Remember the water sits a little below the rim, so the real water volume is slightly less than the full capacity.
Add the cylinder body to the cone underneath: V = π r² Hc + ⅓ π r² Hk, where Hc is the straight side and Hk is the cone height. The cone holds a third of what a cylinder of the same height would, so the bottom section fills slowly at first.
More volume tools
Working out capacity for other shapes? These pair well with the tank volume calculator.
Round tanks, with hollow walls.
Volume calculatorEvery 3D shape in one tool.
Rectangular prism volumeBox and fish-tank volume.
Cone volumeCone and frustum capacity.
Sphere volumeRound vessels and balls.
Area calculatorFootprint and surface area.
Filling a different shape?
Switch tank shapes above, or browse the full geometry hub.