Cylinder Volume Gallons Calculator

Enter a cylinder's diameter and height to get its volume in US gallons, UK imperial gallons, liters, and cubic units using V = π × r² × h.

Quick Facts

Volume formula
V = π × r² × h
r = radius = diameter ÷ 2; h = height or length.
US liquid gallon
1 gal = 231 in³ = 3.785411784 L
The gallon used in the United States.
UK imperial gallon
1 gal ≈ 277.42 in³ = 4.54609 L
About 20% larger than a US gallon.
Full capacity only
Gives 100% volume
A partly filled horizontal tank needs a different (segment) formula.

Your Results

Calculated
Volume
-
V = π × r² × h, in cubic units matching your input
US Gallons
-
Volume ÷ 3.785411784 L
UK Imperial Gallons
-
Volume ÷ 4.54609 L
Liters
-
Volume converted to liters

Ready

Enter a diameter, height, and unit, then press Calculate.

Formula and Method for Cylinder Volume in Gallons

Volume of a Cylinder:

V = π × r² × h

r = radius (½ × diameter); h = height or length

A cylinder's volume is the area of its circular cross-section times its height: V = π × r² × h, where r is the radius (half the diameter) and h is the height or length of the cylinder. Because a "gallon" is a unit of volume, this calculator also converts that raw cubic-unit volume into US liquid gallons, UK imperial gallons, and liters — useful for sizing water tanks, propane tanks, drums, pipes, and other cylindrical containers.

How the calculation works

Enter the cylinder's diameter and height (or length, for a tank lying on its side) and choose the unit they're both measured in. The calculator halves the diameter to get the radius, squares it, and multiplies by π and the height to get the raw volume in that unit's cubic form. It then converts every measurement to cubic centimeters internally and applies 1 US gallon = 3.785411784 liters and 1 UK imperial gallon = 4.54609 liters, so the gallon results are correct no matter which unit you picked. Diameter — not radius — is what most people measure with a tape measure across a tank or pipe, so double-check which one you're entering.

Common mistakes

  • Diameter vs. radius: measuring across the cylinder gives the diameter. Using that number directly as the radius doubles the calculated volume — always halve the diameter first.
  • Mixing units: keep diameter and height in the same unit before calculating; entering one in feet and the other in inches produces a badly wrong volume.
  • US vs. UK gallons: a UK imperial gallon is about 20% larger than a US gallon (4.546 L vs 3.785 L) — using the wrong one under- or over-states capacity by roughly a fifth.
  • Partial fill vs. full capacity: this formula gives the cylinder's total (100%) capacity. A horizontal tank filled only partway needs a circular-segment formula, not a simple percentage of this number.

Real-world applications

  • Sizing water storage tanks, cisterns, rain barrels, and well casings
  • Estimating propane, fuel oil, or chemical drum capacity in gallons
  • Calculating pipe or pipeline segment volume for flow, dosing, or flush-out planning
  • Converting aquarium, silo, or cylindrical planter dimensions into fill volume

Frequently Asked Questions

What is the formula for the volume of a cylinder?
V = π × r² × h, where r is the radius (half the diameter) and h is the height or length. For example, a cylinder with a 12-inch diameter (6-inch radius) and 24-inch height has a volume of π × 6² × 24 ≈ 2,714.34 cubic inches.
How do I convert cylinder volume to gallons?
Divide the volume in cubic inches by 231 to get US liquid gallons (1 US gallon = 231 in³), or by about 277.42 to get UK imperial gallons. This calculator converts your diameter and height to cubic centimeters first, then applies 1 US gallon = 3.785411784 liters and 1 UK gallon = 4.54609 liters, so any input unit works.
Does this calculator give the volume for a horizontal (lying-down) tank?
It gives the cylinder's full, 100% capacity regardless of orientation. For a horizontal tank filled only partway, the liquid volume follows a circular-segment formula and is not a simple percentage of the total volume.
What is the difference between a US gallon and a UK imperial gallon?
A US liquid gallon is 231 cubic inches (3.785411784 liters). A UK imperial gallon is larger, at about 277.42 cubic inches (4.54609 liters exactly) — roughly 20% more, so always confirm which gallon a tank spec sheet is using.

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