Tank Volume Calculator
Work out how many gallons or liters are in a horizontal, vertical or rectangular tank from a dipstick depth, plus its full capacity and how full it is.
A tank lying on its side does not fill in a straight line, so its depth is not its percentage. For a 48 in diameter, 72 in long horizontal tank, 18 in of liquid is 193.2 gallons, 34.3% of the 564.0 gallon capacity, while 24 in, exactly half the height, is 282.0 gallons. Upright and box-shaped tanks scale evenly: depth times the floor area.
Results are estimates from the dimensions you enter, rounded to one decimal. The calculator assumes a straight tank with flat ends and a level tank; domed or dished ends, oval cross-sections, a tilt, sludge, fittings or internal baffles change the real figure. For fuel deliveries, billing or regulatory reporting, use the tank maker's calibration chart.
Measure inside the tank. The liquid depth is from the bottom of the tank to the surface, as a dipstick reads it.
Liquid in the tank
193.2 US gallons
- In liters
- 731.3 L
- Full capacity
- 564.0 gal (2,135.0 L)
- Percent full, by volume
- 34.3%
- Room left
- 370.8 gal
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About the Tank Volume Calculator
For an upright cylinder or a box, the liquid is the area of the floor times the depth, so a 10 ft diameter, 12 ft tall vertical tank with 9 ft of water holds 5,287.7 gallons, three quarters of its capacity. A horizontal tank, the kind used for heating oil, diesel or farm water, is different. Its cross-section is a circle, and the liquid fills a circular segment whose area grows slowly near the bottom, fast through the middle and slowly again near the top. The calculator finds that area from the radius and the depth using the circular segment formula (Weisstein, Wolfram MathWorld), then multiplies by the tank's length. In the default 48 by 72 inch tank, 12 in of oil is only 110.3 gallons, 19.6% of the volume, though a quarter of the height. Gallons are US liquid gallons of 231 cubic inches and liters are 1,000 cubic centimeters, both exact. A box-shaped tank 36 by 12 by 16 in holds 26.2 gallons at 14 in deep, 29.9 gallons full.
Frequently asked questions
How do I measure the liquid depth?+
Lower a clean stick straight down through the fill opening until it touches the bottom, pull it out and measure the wet part. That length, from the bottom of the tank to the surface, is the depth to enter. Use inside dimensions for the tank itself if you can, since the wall takes up a little room.
Why is half the height exactly half full but a quarter is not a quarter?+
A horizontal tank is a circle in cross-section, which is narrow at the bottom and widest in the middle. The first quarter of the depth covers a thin sliver, so in the 48 inch tank 12 in holds 110.3 gallons, not a quarter of 564.0. By symmetry the halfway mark is always exactly half.
Does this work for tanks with rounded or dished ends?+
It treats a horizontal tank as a straight cylinder with flat ends. Tanks with domed or dished ends usually hold a little more than that, so for those the result is an estimate. Some oil tanks are oval or obround in cross-section, which this calculator does not model.
How do I convert the result to liters?+
The calculator shows both. A US gallon is exactly 231 cubic inches, about 3.785 liters, and the liter figure is computed from the same exact volume rather than from the rounded gallons.
Segment area: Weisstein EW, "Circular Segment," MathWorld. Units: NIST Handbook 44, Appendix C.
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