Tank Volume Calculator
Use the Tank Volume Calculator to calculate the capacity of a cylindrical tank from its diameter and height. Enter the tank dimensions in feet to get the volume in gallons, along with the intermediate volume in cubic feet. This calculator is useful for estimating the capacity of water tanks, storage tanks, fuel tanks, and other cylindrical containers.
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The result shows the estimated capacity of the cylindrical tank in US gallons. The calculation also displays the intermediate volume in cubic feet so you can verify how the final result was obtained. Results assume a perfect cylinder and use the internal tank dimensions entered above.
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How Tank Volume Is Calculated
Cylindrical tank volume follows the standard cylinder volume formula — the circular cross-sectional area multiplied by the tank's length or height.
How to Calculate Tank Volume
Volume = π × Radius² × Height (or Length, for a horizontal tank).
Tank Volume Calculator Formula
- Volume (cubic units) = π × Radius² × Height
- Volume (gallons) = Volume (cubic feet) × 7.48052
Why Does the Gallon Conversion Factor Matter?
Because tank volume is naturally calculated in cubic feet or cubic meters from the dimensions, but tanks are typically specified and purchased by gallon (or liter) capacity — the 7.48052 conversion factor (US gallons per cubic foot) bridges the two.
Tank Volume Examples
2 ft radius, 5 ft height: Volume = π × 2² × 5 ≈ 62.83 cubic feet ≈ 470.01 gallons.
Common Tank Volume Calculation Mistakes
Using diameter instead of radius in the formula — radius is half the diameter, and using diameter directly overstates volume by 4x. Forgetting the gallon conversion factor when comparing to a manufacturer's rated gallon capacity. Not accounting for a horizontal cylindrical tank's actual fill volume at partial fill levels, which isn't a simple linear fraction of total volume (the math for partial horizontal tank volume is more complex than for vertical tanks).
How to Use This Calculator
Enter the internal diameter and height of the cylindrical tank in feet. Use measurements taken from the inside of the tank for the most accurate capacity estimate. The calculator divides the diameter by two to determine the radius, applies the cylinder volume formula, and converts the result from cubic feet to US gallons. Use measurements taken from the inside of the tank for the most accurate capacity estimate. The calculator applies the cylinder volume formula and converts the result from cubic feet to US gallons.
Formula & Methodology
The volume of a cylindrical tank is calculated using the formula V = π × r² × h, where V is volume, r is the internal radius of the tank, and h is the internal height. The result is first calculated in cubic feet. To convert cubic feet to US gallons, the volume is multiplied by 7.48052.
A tank with a 6 ft internal diameter has a radius of 3 ft. Volume = π × 3² × 6 = approximately 169.6 cubic feet. Multiplying by 7.48052 gives approximately 1,269.3 US gallons.
Volume = pi * 3^2 * 6 = 169.6 cu ft = 1,269 gallons.
This calculator assumes the tank is a perfect cylinder with uniform internal dimensions. It does not account for wall thickness, rounded ends, domed heads, internal components, displacement, unusable volume, or required freeboard. For horizontal, rectangular, elliptical, partially filled, or irregular tanks, use a calculator designed for that tank shape.
Results are estimates based on the dimensions entered and standard geometric formulas. Verify measurements, units, usable capacity, and manufacturer specifications before using the result for engineering, construction, fuel storage, chemical storage, or other safety-critical applications.
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Frequently Asked Questions
- How do you calculate the volume of a cylindrical tank?
- Divide the tank's internal diameter by two to find the radius. Then multiply pi by the square of the radius and by the internal height: V = π × r² × h. If the measurements are in feet, multiply the result by 7.48052 to convert cubic feet to US gallons.
- How many gallons are in one cubic foot of tank volume?
- One cubic foot equals approximately 7.48052 US gallons. This calculator first determines the tank volume in cubic feet and then applies this conversion factor to calculate capacity in gallons.
- Should I use inside or outside tank dimensions?
- Use internal tank dimensions when estimating actual tank capacity. Outside dimensions include the tank wall thickness and can overestimate the usable internal volume.
- Can I calculate the volume of a horizontal tank with this calculator?
- This calculator is designed for upright cylindrical tanks using radius and height. A horizontal cylindrical tank, especially when partially filled, requires a different formula based on tank length, radius, and liquid depth.
- Does this calculator show total capacity or usable capacity?
- The result represents the theoretical total internal volume of a perfect cylinder. Actual usable capacity may be lower because of freeboard requirements, internal components, tank shape, outlets, and manufacturer specifications.
Last updated 7/15/2026