Tank Volume Calculator
Instantly calculate the capacity of your rectangular, cylindrical, or conical tank. Enter dimensions below to find the total volume in gallons, liters, and cubic meters.
Whether you are sizing a water storage system, installing a fuel tank, or building an aquarium, calculating exact tank capacity is essential. The tank volume calculator above provides instant, mathematically precise volume measurements based on your specific tank shape and dimensions.
Unlike basic formulas that leave you guessing between US gallons, Imperial gallons, and liters, this tool performs exact unit conversions automatically, preventing costly material mistakes and dangerous overflow errors.
How to Calculate Tank Volume (Formulas by Shape)
To calculate the capacity of any storage tank, you must first calculate its geometric volume, usually in cubic inches, cubic feet, or cubic meters. Once the volume is known, you multiply by a conversion factor to find the liquid capacity (gallons or liters).
1. Rectangular & Square Tank Volume Formula
Rectangular tanks (often called rectangular prisms) are the simplest to calculate. This shape is common for custom aquariums, fuel reservoirs, and localized water tanks.
Volume of a Rectangular Tank
Example: For a tank measuring 24 inches long, 16 inches wide, and 12 inches high, the volume is: 24 × 16 × 12 = 4,608 cubic inches.
To convert cubic inches to US Liquid Gallons, divide the result by 231. 4,608 ÷ 231 = 19.95 gallons (commonly sold as a 20-gallon tank).
2. Cylindrical Tank Volume Calculator (Vertical & Horizontal)
Cylindrical tanks are widely used for rainwater harvesting, propane storage, and industrial chemicals because the curved shape inherently resists internal pressure better than flat walls.
Volume of a Cylindrical Tank
Where:
- π (Pi) ≈ 3.14159
- r (Radius) = Diameter ÷ 2
- h (Height or Length) = The total length of the cylinder
Whether the cylinder is positioned vertically (standing up) or horizontally (laying down), the total volume calculation remains exactly the same. Note: If you are calculating a partially filled horizontal cylinder, the math becomes significantly more complex, requiring circular segment calculations.
3. Capsule Tank Volume
A capsule tank consists of a straight central cylinder with a hemisphere (half-sphere) cap on each end. It is standard for pressurized gas storage, such as residential propane tanks.
Volume of a Capsule Tank
This formula simply combines the volume of the middle cylinder (πr²h) with the volume of a complete sphere (4/3πr³), representing the two end caps combined.
Standard Tank Size & Capacity Chart
If you are purchasing a pre-built glass aquarium or a standard poly water tank, use this quick reference table to find the capacity in gallons and liters for commonly searched dimensions.
| Dimensions (L × W × H) | Shape Type | Volume (US Gallons) | Volume (Liters) |
|---|---|---|---|
| 20″ × 10″ × 12″ | Rectangular | 10.39 gal | 39.3 L |
| 24″ × 16″ × 12″ | Rectangular | 19.95 gal | 75.5 L |
| 30″ × 12″ × 19″ | Rectangular | 29.61 gal | 112.1 L |
| 30″ × 13″ × 13″ | Rectangular | 21.95 gal | 83.1 L |
| 36″ × 12″ × 18″ | Rectangular | 33.66 gal | 127.4 L |
| 60″ × 24″ × 24″ | Rectangular | 149.61 gal | 566.3 L |
| 4 ft × 4 ft × 4 ft | Square/Cube | 478.75 gal | 1,812.3 L |
| 5 ft × 5 ft × 5 ft | Square/Cube | 935.06 gal | 3,539.6 L |
How to Measure Your Tank Accurately
The most common mistake when using a tank volume calculator is failing to account for wall thickness. Liquid fills the interior volume of the tank, not the exterior footprint.
- Always use interior dimensions: If you measure the outside of a heavy-duty plastic tank or a thick glass aquarium, subtract the thickness of the walls (multiplied by two) from your length and width measurements.
- Account for safe fill lines: Very few tanks are filled to the absolute brim. If you want to know the usable water tank capacity, measure the height up to the overflow pipe or safe fill line, not the total physical height of the tank.
- Stay consistent with units: Never mix inches and feet. If your tank is 4 feet long and 18 inches wide, convert everything to inches (48 inches length, 18 inches width) or everything to feet (4 feet length, 1.5 feet width) before calculating. The calculator above handles this automatically if you stick to one input unit.
Gallons, Liters, and Cubic Meters Explained
Volume conversion can be tricky because terms like “gallon” mean different things depending on your location and industry.
US Liquid Gallon vs Imperial Gallon
The US Liquid Gallon is legally defined as exactly 231 cubic inches, which equals roughly 3.785 liters. This is the standard measurement for fuel and water in the United States.
The UK Imperial Gallon is approximately 20% larger than the US gallon. It is defined as 4.54609 liters. If you are reading a spec sheet from the UK, Canada, or Australia, always clarify which gallon they are referencing. (Our calculator explicitly separates US Gallons and UK Gallons in the results panel to prevent this confusion).
The Metric System Advantage (Liters and Cubic Meters)
In the metric system, calculating a water tank liter calculator is beautifully simple due to base-10 physics:
- 1 cubic centimeter (cm³) = 1 milliliter (mL)
- 1,000 cubic centimeters = 1 Liter (L)
- 1 cubic meter (m³) = 1,000 Liters (L)
Furthermore, pure water has a density of roughly 1 kg per liter. This means a 1,000-liter tank (1 cubic meter) of water weighs precisely 1,000 kilograms (1 metric tonne), making structural weight load calculations incredibly easy compared to the US customary system.
Worked Examples of Tank Volume Calculations
Example 1: How to find the capacity of a cylindrical water tank in liters
Suppose you have a vertical round water tank that is 2 meters in diameter and 3 meters tall.
1. Find the radius: 2m ÷ 2 = 1 meter.
2. Apply the formula: V = π × r² × h
3. V = 3.14159 × (1²) × 3 = 9.4247 cubic meters.
4. Convert to liters: 9.4247 × 1000 = 9,424.7 Liters.
Example 2: Calculating a rectangular septic tank volume in gallons
You have a rectangular concrete septic tank that measures 8 feet long, 4 feet wide, and 5 feet deep.
1. Apply the formula: V = L × W × H
2. V = 8 × 4 × 5 = 160 cubic feet.
3. Since 1 cubic foot equals roughly 7.48 US gallons, multiply: 160 × 7.48 = 1,196.8 US Gallons (this would be sold as a 1,200-gallon septic tank).
Frequently Asked Questions
Reference: https://en.wikipedia.org/wiki/Stone_slab