Tank Volume Calculator
Pick a tank shape, enter the inside dimensions in inches, and get the capacity. A horizontal cylinder 48 inches across and 96 inches long holds 752.02 gallons.
How the tank volume calculator works
Choose the shape of the tank, then enter its inside dimensions in inches. The calculator finds the volume in cubic inches and converts it to U.S. gallons, liters and cubic feet. Use inside measurements, not the outside size, because the wall thickness of steel, plastic or fiberglass takes away from the space that holds liquid.
For a horizontal cylinder, enter the diameter and the length. For a vertical cylinder, enter the diameter and the height. For a rectangular tank, enter the width, the length and the height. The height box is ignored for cylinders. The result is the full capacity with the tank filled to the top, not a partial fill level.
The formulas
One U.S. gallon is defined as 231 cubic inches. A liter is 0.264172 gallons, which is the same as 3.785412 liters per gallon. See the NIST conversion factors for the exact definitions.
Example: A horizontal cylinder with a 48 inch diameter and a 96 inch length has a capacity of 752.02 gallons. That is 2,846.7 liters or 100.53 cubic feet, and the volume is 173,718 cubic inches. These dimensions are an illustration only, so replace them with your own tank.
Limits and tips
The tank is treated as a plain cylinder or box. Domed or dished ends, cone bottoms, internal baffles and fittings are not included, so real capacity can be a little higher or lower than the number shown. A manufacturer rating plate is the best reference for a purchased tank.
Many tanks should not be filled to the brim. Heating oil, fuel and chemical tanks often have a maximum fill level set by the maker or by local rules, so check before you plan a delivery from this figure. For round pools and ponds, try the pool volume calculator. For soil, gravel or concrete volume in cubic yards, use the cubic yard calculator.
Measuring your tank
Measure the inside diameter across the widest point of a round tank, and the inside length or height from end to end. If you can only measure the outside, subtract twice the wall thickness from each dimension. Check the unit before you enter numbers: the fields take inches, so a tank that is 4 feet across is entered as 48.
For a vertical cylinder, each inch of height holds the same amount, so the gallons per inch is the total capacity divided by the height. That makes it easy to turn a dipstick reading into gallons. A horizontal tank does not work that way, because the slice of liquid is widest at the middle and narrow near the top and bottom, so a horizontal tank needs a chart or a segment formula for partial fills.
Converting the result
The calculator reports U.S. gallons, not imperial gallons. An imperial gallon is about 20 percent larger, so confirm which gallon a tank label uses if the tank was made outside the United States. Liters are shown for metric labels and cubic feet for sizing a pad, a pit or a room around the tank.
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Frequently asked questions
How do I calculate the gallons in a horizontal tank?
Multiply 3.14159 by the radius squared, multiply by the length, then divide the cubic inches by 231. A 48 inch by 96 inch horizontal cylinder gives 752.02 gallons.
Does this work for a partly filled tank?
No. It returns the full capacity. A partly filled horizontal cylinder needs a segment formula, and a vertical tank can be scaled by the fill height divided by the total height.
Should I measure inside or outside?
Measure inside. Outside dimensions overstate capacity because they include the wall.
How many liters is that?
Multiply gallons by 3.785412. The default tank holds 2,846.7 liters.
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