Tank Volume Calculator

Find the capacity of a vertical, horizontal, rectangular, capsule, oval or cone-bottom tank, and the volume at any fill height. Results in US gallons, imperial gallons, litres, cubic feet and cubic metres.

About the tank volume calculator

The Tank Volume Calculator works out how much a tank can hold from its inside dimensions. Pick one of six shapes: vertical cylinder, horizontal cylinder, rectangular, capsule, oval or cone bottom. Enter the lengths, and the total capacity appears in US gallons, imperial gallons, litres, cubic feet and cubic metres. Each length has its own unit, so you can type a diameter in inches and a height in feet without converting anything first.

If you also enter a fill height, the calculator reports how full the tank is as a percentage and gives the volume of liquid currently inside, in the same five units. That is useful for checking a dipstick or sight gauge reading, estimating how much is left in a heating oil tank, or working out how much to order to top up a water tank.

How to calculate tank volume

Steps

Choose the shape that matches your tank.
Enter each dimension and pick its unit: feet, inches, yards, metres, centimetres or millimetres. Units can differ from one field to the next.
Measure inside dimensions, not outside ones. Wall thickness takes away real capacity.
Optionally enter a fill height, measured from the lowest inside point. For a cone-bottom tank this is measured from the tip of the cone. It cannot be larger than the inside height, and an inline message names the maximum if it is.
Read the total capacity, and the percent full and filled volume if you gave a fill height.

Formulas for each shape

Full tanks

Vertical cylinder with radius $r$ and height $h$ :

V = \pi r^2 h

Rectangular with length $L$ , width $W$ and height $H$ :

V = L \times W \times H

Capsule with radius $r$ and overall length $L$ , where the two hemispherical ends together make one sphere:

V = \pi r^2 (L - 2r) + \frac{4}{3}\pi r^3

Oval, a horizontal elliptical cross-section with width $W$ , height $H$ and length $L$ :

V = \pi \frac{W}{2} \frac{H}{2} L

Cone bottom with a straight wall of height $w$ above a cone of height $c$ :

V = \pi r^2 \left( w + \frac{c}{3} \right)

Partly filled tanks

A horizontal cylinder filled to height $h$ has a circular segment as its cross-section, multiplied by the length:

V = L \left[ r^2 \arccos\left(\frac{r-h}{r}\right) - (r-h)\sqrt{2rh - h^2} \right]

A capsule adds the partial sphere cap at the ends, $\pi h^2 (3r - h)/3$ . An oval uses the same segment with $r = H/2$ , scaled by $W/H$ . A cone bottom filled to height $h$ inside the cone holds

V = \frac{\pi r^2 h^3}{3 c^2}

and above the cone it holds $\pi r^2 c/3 + \pi r^2 (h - c)$ .

Worked examples

Vertical cylinder. A tank 6 ft across and 8 ft tall holds 226.19 cubic feet, which is 1,692.1 US gallons, 1,409.1 imperial gallons or 6,405.2 litres. Filled to 4 ft it holds 113.10 cubic feet, exactly 50 percent.

Horizontal cylinder. A tank 4 ft in diameter and 10 ft long holds 125.66 cubic feet. Filled to 2 ft, half the diameter, it is exactly 50 percent. Filled to 1 ft, a quarter of the diameter, it holds 24.57 cubic feet, which is only 19.6 percent, not 25 percent. The bottom of a round tank is narrow, so the first few inches hold little.

Rectangular. A box 4 ft by 3 ft by 2 ft holds 24 cubic feet, or 179.5 US gallons, 149.5 imperial gallons and 679.6 litres.

Capsule. A tank 2 ft in diameter and 8 ft overall is a 6 ft cylinder plus a 2 ft sphere, giving 23.04 cubic feet.

Oval. A tank 4 ft wide, 2 ft high and 10 ft long holds 62.83 cubic feet. Filled to 1 ft it holds 31.42 cubic feet, which is 50 percent.

Cone bottom. A tank 4 ft across with a 6 ft straight wall and a 3 ft cone holds 87.96 cubic feet. Filled to 3 ft, just the cone, it holds 12.57 cubic feet. Filled to 1 ft it holds only 0.47 cubic feet. Filled to 5 ft it holds 12.57 plus 25.13, which is 37.70 cubic feet.

Mixed units. A rectangular tank 2 m by 50 cm by 1000 mm is 1 cubic metre, or 1,000 litres.

Units and conversions

The calculator uses 1 US gallon as 231 cubic inches, or 3.785411784 litres, and 1 imperial gallon as 4.54609 litres. One cubic foot is about 7.4805 US gallons or 28.3168 litres. If you need other volume units, such as barrels, quarts or cups, the Volume Converter handles them, and the Length Converter helps if your tape measure uses a different unit from your plans.

Accuracy and limits

The result is a geometric capacity based on the dimensions you enter. Real tanks have fittings, internal baffles, wall thickness, dished or domed ends and outlets that sit above the true bottom, so the usable volume is often lower than the nominal figure. Always measure inside dimensions and compare the answer with the manufacturer's rating. For anything safety related, such as fuel storage or chemical dosing, rely on the labelled capacity and local regulations.

Privacy

Nothing is uploaded; every calculation runs in your browser and never leaves your device.

Related tools

For a tank that is a plain cylinder, try the Cylinder Tank Volume Calculator, and for boxes and aquariums the Rectangular Tank Volume Calculator. To find the footprint of a tank pad or bund, use the Area Calculator. For pouring a base slab, the Concrete Calculator estimates the volume you need.

Frequently asked questions

Which tank shapes does this calculator support?

Six shapes: vertical cylinder, horizontal cylinder, rectangular, capsule with hemispherical ends, oval with a horizontal elliptical cross-section, and cone bottom. Each shape asks only for the dimensions it needs.

Should I measure inside or outside dimensions?

Measure inside dimensions. Wall thickness reduces the space available for liquid, so using outside measurements overstates the capacity, especially on small tanks with thick walls.

How do I work out how much liquid is in a partly filled tank?

Enter the fill height, measured from the lowest inside point of the tank. For a cone-bottom tank, measure from the tip of the cone. The calculator then shows the percent full and the filled volume in US gallons, imperial gallons, litres, cubic feet and cubic metres.

Why is a horizontal tank filled to a quarter of its diameter less than 25 percent full?

A round cross-section is narrow at the bottom, so the first part of the depth holds little liquid. A 4 ft diameter, 10 ft long horizontal tank filled to 1 ft holds 24.57 cubic feet, which is 19.6 percent of its 125.66 cubic foot capacity.

What is the difference between US and imperial gallons?

A US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, so an imperial gallon is about 20 percent larger. The calculator shows both so you can match the unit on your tank label or supplier invoice.

Is the result the same as the manufacturer's rated capacity?

Not always. The result is geometric and ignores fittings, baffles, dished ends and outlets above the bottom. Treat it as an estimate and check the manufacturer's rating for the usable volume.

Is my data sent anywhere?

No. The tank capacity and fill level sums run in your browser, so your tank dimensions and fill height are never uploaded or stored on a server. They stay on this device and are not shared with anyone.

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