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Cylinder Volume in Gallons Calculator

Determining how much liquid a cylindrical tank can hold requires converting cubic measurements into gallons—a common task in engineering, agriculture, and industrial applications. This calculator handles the mathematics and unit conversions automatically, accepting radius or diameter alongside height in any standard measurement system. Whether you're sizing a propane tank, designing a water storage vessel, or estimating capacity for a chemical storage drum, this tool delivers accurate results in both US and UK gallons.

Last updated: April 20, 2026

Creators Mateusz Mucha, BEng

Reviewers Anna Szczepanek and Jasmine J. Mah

3,624 people find this calculator helpful

Cylinder Volume Formula

The volume of a cylinder depends on its cross-sectional area and height. Once calculated in cubic units, the result converts to gallons using standard conversion factors.

V = π × r² × h

d = 2 × r

V — Volume of the cylinder
r — Radius of the circular base
h — Height of the cylinder
d — Diameter of the circular base

Understanding Gallon Conversions

A gallon represents volume, but the exact quantity differs between measurement systems. The US gallon equals 231 cubic inches or 3.785 litres, while the UK (imperial) gallon contains 277.4 cubic inches or 4.546 litres.

When your radius and height are measured in feet, first calculate volume in cubic feet, then multiply by the appropriate conversion factor:

US gallons: cubic feet × 7.481
UK gallons: cubic feet × 6.229

If measurements are in inches, convert cubic inches by dividing by 231 (US) or 277.4 (UK). Metric measurements in centimetres require converting cubic centimetres by dividing by 3,785 (US) or 4,546 (UK).

Step-by-Step Calculation Example

Suppose you have a cylindrical tank with a radius of 2 feet and a height of 5 feet. Working through the calculation:

Square the radius: 2² = 4
Multiply by π: 4 × 3.14159 = 12.566
Multiply by height: 12.566 × 5 = 62.83 cubic feet
Convert to US gallons: 62.83 × 7.481 = 470.1 gallons

The same tank holds approximately 389 UK gallons. Diameter-based calculations simply require dividing the diameter by two before squaring.

Common Pitfalls to Avoid

Accurate volume calculations depend on careful measurement and unit consistency.

Mixing Units — Never combine measurements in different systems. If height is in feet, ensure radius is also in feet. Converting partway through introduces errors; standardise all inputs first.
Measuring the Right Values — Measure the interior radius for capacity calculations, not the exterior dimension. Wall thickness matters for storage vessels—always use inside dimensions to determine usable volume.
Rounding Conversion Factors — Use precise conversion factors (7.481 for US gallons from cubic feet, not 7.5). Small rounding errors compound, especially with larger tank volumes.
Confusing Radius and Diameter — Radius is half the diameter. Squaring the wrong value dramatically changes results. Verify which measurement you've taken before entering it into the calculator.

Practical Applications

Cylindrical volumes in gallons appear across numerous industries. Farmers size irrigation tanks to match seasonal rainfall and crop water needs. Breweries calculate fermentation vessel capacities in gallons to scale recipes and production batches. Industrial plants dimension storage drums for chemicals, oils, and solvents based on gallon requirements. Residential water heaters are typically rated in gallons, helping homeowners select appropriately sized units. Pool maintenance professionals calculate total water volume in gallons to determine chemical dosing rates.

Frequently Asked Questions

What's the difference between US and UK gallons, and how do I know which to use?

A US gallon contains 3.785 litres, while a UK (imperial) gallon holds 4.546 litres—about 20% more. The UK gallon is larger, so the same volume in cubic units yields fewer UK gallons than US gallons. Most North American applications use US gallons. British and Commonwealth countries typically employ UK gallons. Check your equipment specifications or local standards to confirm which unit applies to your project.

Can I calculate cylinder volume if I only know the diameter, not the radius?

Absolutely. The diameter is simply twice the radius, so divide your diameter measurement by two to get the radius, then proceed with the standard formula. For example, a cylinder with a 6-inch diameter has a 3-inch radius. The calculator handles this conversion automatically, but knowing the relationship helps you understand what's happening behind the scenes.

How accurate does my measurement need to be for reliable results?

Measurement precision should match your tolerance for error. For approximate estimates, measuring to the nearest inch or centimetre usually suffices. Industrial applications requiring high accuracy demand measurements to the nearest tenth of an inch. Small measurement errors magnify when squared (in the radius term), so a 10% error in radius produces roughly a 20% error in final volume. Invest in proper measuring tools if precision is critical.

Why is the volume formula different for cylinders compared to other shapes?

The formula V = π × r² × h reflects the cylinder's geometry. The radius squared (r²) calculates the circular base area, while π accounts for the circle's shape. Multiplying by height extends that base area vertically through the full length of the cylinder. Rectangular prisms use length × width × height because their bases have straight edges; cylinders require π because circles are fundamentally different.

How do I convert from other volume units like cubic meters or litres to gallons?

One cubic meter equals 264.17 US gallons or 219.97 UK gallons. One litre equals 0.264 US gallons or 0.220 UK gallons. If your cylinder volume is calculated in litres, multiply by these factors to get gallons. The calculator accepts metric inputs directly and handles the conversion, but these ratios help you verify results or work problems by hand.

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