Cylinder Tank Volume Calculator (Gallons and Litres)
Find the capacity of a vertical or horizontal cylinder tank in US gallons, imperial gallons, litres, cubic feet and cubic metres, and see how much liquid is in it at any fill height.
Measured from the lowest inside point.
Enter the dimensions to see the volume.
About the cylinder tank volume calculator
The Cylinder Tank Volume Calculator finds the capacity of a round tank from its diameter and its height or length. It opens with a vertical cylinder selected, the shape of most water tanks, silos and storage drums standing on end. Switch to a horizontal cylinder for fuel tanks, septic tanks and tankers lying on their side. Results appear in US gallons, imperial gallons, litres, cubic feet and cubic metres, and every length can be typed in its own unit.
Add a fill height to see how full the tank is right now. This matters most for horizontal tanks, where the relationship between depth and volume is not a straight line.
How to calculate cylinder tank volume
Steps
- Pick Vertical cylinder if the axis of the tank is upright, or Horizontal cylinder if it lies flat.
- Enter the inside diameter and the height (vertical) or length (horizontal). Pick a unit for each.
- Measure inside the tank. Subtract the wall thickness if you only have outside figures.
- Optionally enter the fill height, measured from the lowest inside point. For a vertical tank that is the liquid depth; for a horizontal tank it is the depth at the deepest point, measured straight down from the surface to the bottom of the shell.
- Read the total capacity, then the percent full and filled volume.
Cylinder formulas
Vertical cylinder
Volume is the area of the circular base times the height, with radius equal to half the diameter:
Because the sides are straight, a partly filled vertical tank is just the same formula with the liquid depth in place of . Half the height means half the volume.
Horizontal cylinder
A full horizontal tank uses the same . A partly filled one needs the area of a circular segment, the slice of the circle under the liquid surface, multiplied by the length :
Here is the liquid depth and is the radius. At the expression gives exactly half of , and at it gives the full volume.
Worked example: a vertical water tank
A tank 6 ft in diameter and 8 ft tall has a radius of 3 ft. The volume is , which is 226.19 cubic feet. That converts to 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.
Worked example: a horizontal fuel tank
A horizontal tank 4 ft in diameter and 10 ft long holds 125.66 cubic feet when full. Now check the depth readings.
- Filled to 2 ft, which is half the diameter, it is exactly 50 percent full.
- Filled to 1 ft, a quarter of the diameter, it holds 24.57 cubic feet. That is only 19.6 percent, not 25 percent.
The reason is the curved bottom. Near the base the tank is narrow, so each inch of depth adds little volume. Near the middle the tank is at its widest, so each inch adds the most. A dipstick marked in even steps therefore needs a conversion chart, and this calculator builds that chart one reading at a time.
Vertical or horizontal: which is which
A tank is vertical when the circular ends are the top and bottom. It is horizontal when the circular ends are the sides. The same tank gives the same total volume either way, but the partial fill is very different. If you are not sure, look at where the fill pipe and the gauge sit and use the dimension that runs along the straight side as the height or length.
Converting the result
If you need barrels, quarts or other units, the Volume Converter converts the result. If your dimensions come as a mix of inches and centimetres, the Length Converter can tidy them first, though the calculator also accepts mixed units directly.
Accuracy and limits
The result is geometric and assumes a perfect cylinder with flat ends. Many real tanks have dished, domed or conical ends, internal baffles, manways and fittings, and their outlet may sit above the true bottom, so the usable volume is usually lower than the nominal one. Measure the inside diameter, and check the manufacturer's rating before relying on a figure for fuel, chemicals or any regulated use. If your tank has hemispherical ends, the capsule shape on the Tank Volume Calculator fits better.
Privacy
Nothing is uploaded; every calculation runs in your browser and never leaves your device.
Related tools
The Tank Volume Calculator covers six shapes, including capsule, oval and cone bottom tanks. For box-shaped tanks use the Rectangular Tank Volume Calculator. To size a base, the Area Calculator gives the footprint and the Concrete Calculator estimates the pour.
Frequently asked questions
How do I calculate the volume of a cylinder tank?
Multiply the area of the circular cross-section by the height or length. In symbols that is pi times the radius squared times the height. Enter the inside diameter and the height or length, and the calculator converts the result to gallons, litres and cubic units.
What is the difference between a vertical and a horizontal cylinder tank?
The total volume is the same formula for both, but the orientation changes how fill depth relates to volume. In a vertical tank, half the height means half the volume. In a horizontal tank the relationship is curved because the cross-section is a circle.
Why is a horizontal tank at a quarter of its diameter not 25 percent full?
The curved bottom is narrow, so the first inches of depth hold little liquid. For a 4 ft diameter, 10 ft long tank, 1 ft of liquid is 24.57 cubic feet, or 19.6 percent of the 125.66 cubic feet total. Only at half the diameter is it exactly 50 percent.
Where do I measure the fill height?
Measure from the lowest point inside the tank up to the liquid surface. For a horizontal tank that is the depth at the deepest point, and it cannot exceed the inside diameter. If it does, the calculator shows an error naming the maximum.
Does the calculator account for dished or domed tank ends?
No. It treats the tank as a plain cylinder with flat ends, so a tank with dished ends holds somewhat more or less than shown depending on the shape. If your ends are hemispherical, use the capsule shape on the main tank volume calculator, and check the manufacturer's rating either way.
Why does my tank hold less than the calculated volume?
The figure is geometric. Wall thickness, fittings, baffles and outlets that sit above the true bottom all reduce the usable volume, and many tanks are filled to a safe level that is below the brim. Measure the inside diameter and compare the result with the labelled capacity.
Is my data sent anywhere?
No. The cylinder capacity and partial fill sums run in your browser, so your diameter, length and liquid level are never uploaded or stored on a server. They stay on this device and are not shared with anyone.