Cylinder Volume Calculator Gallons: How to Use

This calculator works out the volume of a cylinder in US gallons when you enter its diameter (or radius) and height. You get the result in gallons, plus the volume in cubic feet and liters for easy reference. It uses the standard formula for cylinder volume and converts the cubic result into gallons.

Formula

The volume of a cylinder is the area of its circular base times its height. In symbols:

V = π × r² × h

where:

• V = volume (cubic feet, cubic meters, etc.)
• Ï€ ≈ 3.14159
• r = radius of the base (half the diameter)
• h = height of the cylinder

To get gallons, you then multiply the cubic volume by the conversion factor. One US gallon is exactly 231 cubic inches, which equals 0.133681 cubic feet. So if your dimensions are in feet, the formula becomes:

Gallons = π × (d/2)² × h × 7.48052

where d is the diameter in feet, h is the height in feet, and 7.48052 is the number of US gallons in one cubic foot. If you measure in inches, use the factor 0.004329 (gallons per cubic inch).

Worked Example

Using the default values from the calculator: a cylinder with a diameter of 3 feet and a height of 5 feet.

1. Radius = diameter ÷ 2 = 3 ÷ 2 = 1.5 ft
2. Base area = π × r² = 3.14159 × (1.5)² = 3.14159 × 2.25 = 7.06858 ft²
3. Volume in cubic feet = base area × height = 7.06858 × 5 = 35.3429 ft³
4. Convert to gallons: 35.3429 × 7.48052 = 264.4 gallons

The calculator shows 264.4 gallons, matching this step-by-step result. The same volume is 35.34 cubic feet or 1001.1 liters.

When to Use This Calculator

You might need cylinder volume in gallons for a variety of real-world tasks:

• Figuring out how much water a vertical storage tank holds
• Sizing a rainwater collection barrel or cistern
• Estimating the capacity of a propane or oil tank
• Calculating the volume of a pipe or well casing
• Determining how much liquid a cylindrical container can hold for shipping or brewing

The calculator works for any cylinder, whether it stands upright or lies on its side. It gives the total volume when full. If you need the volume at a partial fill, that requires a different formula that accounts for the liquid depth.

How to Read the Results

The main result is in US gallons. The calculator also shows cubic feet and liters so you can compare with other measurements. Note that US gallons are different from imperial gallons (used in the UK and some Commonwealth countries). One US gallon is 3.78541 liters, while one imperial gallon is 4.54609 liters. If you need imperial gallons, multiply the US gallon result by 0.832674.

For practical purposes, a gallon of water weighs about 8.34 pounds. So if you fill a 264-gallon tank, the water alone weighs roughly 2,200 pounds. That weight matters for structural support, vehicle loads, or shipping costs.

Common Mistakes and How to Avoid Them

The most frequent error is mixing units. If you enter the diameter in inches and the height in feet, the volume will be wrong. Always use the same unit for both dimensions. The calculator assumes feet, but you can convert easily:

• 1 foot = 12 inches
• 1 inch = 0.08333 feet
• 1 meter = 3.28084 feet

Another common mistake is using the diameter instead of the radius in the formula. The formula uses radius, but the calculator asks for diameter and divides by two internally. If you do the math yourself, remember to halve the diameter first.

Also, be careful with the difference between radius and diameter when measuring. A tank that is 2 feet across has a radius of 1 foot. Using 2 feet as the radius would give four times the actual volume.

Limits of the Formula

The formula assumes a perfect right circular cylinder with a constant cross-section. Real tanks often have domed or dished ends, which add volume beyond the straight cylindrical section. For example, a propane tank with hemispherical heads holds more than a plain cylinder of the same length and diameter. The calculator only covers the cylindrical part.

Also, the formula gives the total volume when full. If you need the volume at a specific liquid level (like a partially filled tank), you need a more complex formula involving the inverse cosine of the liquid height. That is beyond this simple calculator.

Finally, the conversion factor is for US gallons. If you are using imperial gallons, the result will be about 20% too high. Always confirm which gallon your application uses.

Frequently Asked Questions

How do I convert cubic feet to gallons?

Multiply the cubic feet by 7.48052 to get US gallons. For example, 10 cubic feet × 7.48052 = 74.8 gallons. If you have cubic inches, multiply by 0.004329.

What is the difference between US and imperial gallons?

A US gallon is 231 cubic inches (about 3.785 liters). An imperial gallon is 277.42 cubic inches (about 4.546 liters). Imperial gallons are about 20% larger. To convert US gallons to imperial, multiply by 0.832674.

Can I use this for a horizontal cylinder?

Yes, the total volume is the same regardless of orientation. However, if you need the volume at a partial fill, the calculation changes. For a horizontal cylinder, the filled volume depends on the liquid height and the diameter, requiring a different formula.

How do I measure a tank that has rounded ends?

Measure the straight cylindrical section and calculate its volume with this calculator. Then add the volume of the end caps separately. For hemispherical ends, the volume of each cap is (2/3)Ï€r³. For elliptical or dished ends, use the manufacturer’s specifications.

Why does my result differ from the tank’s label?

Manufacturers often label tanks with a nominal capacity that includes some extra space or uses different dimensions. Also, the actual dimensions may be slightly different from the nominal ones. Always measure the actual inside dimensions for accurate volume.

Related

• Area Calculator: Inches to Square Feet
• Area Calculator in Feet: How to Use It
• Area Calculator Cubic Feet: How to Find Volume

in d | Diameter | ft | 3 | 0
in h | Height | ft | 5 | 0
out gal | Volume (US gallons) | gal | (pi * (d/2)^2 * h) * 7.48052 | 1
out ft3 | Volume (cubic feet) | ft³ | pi * (d/2)^2 * h | 2
out l | Volume (liters) | L | (pi * (d/2)^2 * h) * 28.3168 | 1