Cylinder Tank Volume Calculator Gallons

This calculator works out the volume of a vertical or horizontal cylinder tank in US gallons. You enter the tank diameter and length (or height) in inches or feet, and it returns the total capacity in gallons, plus the volume in cubic feet and liters as a cross-check.

Formula

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

V = π × r² × h

Where:

• V = volume in cubic inches (in³)
• π ≈ 3.14159
• r = radius of the tank = diameter ÷ 2, in inches
• h = length or height of the tank, in inches

To convert cubic inches to US gallons, divide by 231 (since 1 US gallon = 231 in³). For cubic feet, divide by 1,728 (1 ft³ = 1,728 in³). For liters, multiply the gallon result by 3.78541.

Worked Example

Using the default values: a tank with a 48-inch diameter and 96-inch length.

1. Radius = 48 ÷ 2 = 24 inches
2. Area of base = π × 24² = 3.14159 × 576 = 1,809.56 in²
3. Volume in cubic inches = 1,809.56 × 96 = 173,717.76 in³
4. Convert to gallons: 173,717.76 ÷ 231 = 752.0 gallons

The calculator shows 752.0 US gallons, matching the step-by-step result.

When to Use This Calculator

This applies to any full cylinder tank: water storage tanks, propane tanks, fuel tanks, air receiver tanks, or cylindrical process vessels. It assumes the tank is completely full. If you need the volume at a partial fill level, this calculator won’t give that — you’d need a horizontal cylinder segment formula or a dip chart.

For horizontal tanks, the same formula works if the tank is completely full. For partially filled horizontal tanks, the volume depends on the liquid height, not just the diameter and length. That requires a more complex calculation involving the circular segment area.

Common Mistakes and How to Avoid Them

• Mixing units: If you enter diameter in feet and length in inches, the result is wrong. Convert everything to the same unit first (inches is easiest for gallon conversion).
• Using radius instead of diameter: The calculator asks for diameter; if you enter the radius, the volume will be one-quarter of the actual value.
• Forgetting wall thickness: The formula uses outer dimensions. For thick-walled tanks, the internal volume is smaller. Use internal diameter and length for accuracy.
• US vs. Imperial gallons: This calculator uses US gallons (231 in³). Imperial gallons are larger (277.42 in³). If you need imperial gallons, multiply the US gallon result by 0.83267.

How to Read the Results

The first result, in gallons, is the total capacity when full. The cubic feet value helps when comparing with tank specs that list volume in ft³. The liters value is useful for metric comparisons or when mixing with equipment rated in liters.

For example, a 752-gallon tank holds about 2,846 liters. That’s roughly 6,000 pounds of water (water weighs 8.34 lbs per gallon), so make sure the supporting structure can handle the weight when full.

Practical Considerations

Real tanks are never perfectly cylindrical — there are rounded ends, dished heads, or domed tops. The formula gives the volume of the straight cylindrical section only. For tanks with elliptical or hemispherical heads, add the head volume separately. A common rule for dished heads is to add about 10–15% to the cylinder volume, but exact values depend on the head shape.

Also, tanks are rarely filled to 100% capacity. Many have a maximum fill level (e.g., 90% for fuel tanks to allow for expansion). Always check the manufacturer’s fill limit for safety and legal compliance.

Frequently Asked Questions

How many gallons is a 48×96 tank?

Using the formula: radius = 24 in, area = π×24² = 1,809.56 in², times 96 in = 173,717.76 in³, divided by 231 = 752.0 US gallons. That’s the default example above.

How do I calculate gallons from cubic inches?

Divide the cubic inch volume by 231. For example, 1,000 in³ ÷ 231 = 4.33 US gallons. For liters, multiply the cubic inches by 0.016387.

Does this work for horizontal tanks?

Yes, for a full horizontal tank. The orientation doesn’t change the total volume — only the partial fill calculation differs. For partial fills, you need the liquid height and a segment area formula.

What’s the difference between US and imperial gallons?

A US gallon is 231 cubic inches (3.785 liters). An imperial gallon is 277.42 cubic inches (4.546 liters). To convert US gallons to imperial, multiply by 0.83267. Most fuel and water measurements in the US use US gallons.

Why does my tank label say a different capacity?

Manufacturers often list nominal capacity based on the shell dimensions, but the actual usable volume may be less due to internal fittings, baffles, or head shapes. Also, some labels use rounded numbers (e.g., 750 gal) for a tank that actually holds 752. Always use internal dimensions for the most accurate number.

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in d | Tank diameter | in | 48 | 0
in L | Tank length/height | in | 96 | 0
out gal | Volume (US gallons) | gal | (pi * (d/2)^2 * L) / 231 | 1
out ft3 | Volume (cubic feet) | ft³ | pi * (d/2)^2 * L / 1728 | 1
out L | Volume (liters) | L | (pi * (d/2)^2 * L) / 231 * 3.78541 | 1