How to Calculate Tank Volume: Formulas for Cylindrical, Rectangular, and Cone Tanks
Calculate tank volume using the correct formula for your tank shape — cylindrical, rectangular, horizontal cylinder, or cone. Includes unit conversion and partial fill calculations.
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Tank Volume Calculation Overview
Tank volume depends on the tank's geometry. Choosing the wrong formula gives significantly wrong results. Identify your tank shape first, then apply the appropriate formula.
Cylindrical Tank Volume (Vertical)
Most propane tanks, water towers, and storage tanks are vertical cylinders.
Formula: V = π × r² × h
Where r = radius (diameter ÷ 2) and h = height
Example: Cylindrical tank, diameter = 4 ft, height = 6 ft: - Radius = 4 ÷ 2 = 2 ft - V = π × 2² × 6 = π × 4 × 6 = 75.40 cubic feet - To convert to gallons: 75.40 × 7.48 = 564 gallons
Rectangular (Box) Tank Volume
Above-ground plastic storage tanks, aquariums, or square concrete tanks.
Formula: V = L × W × H
Example: Tank 4 ft long × 2 ft wide × 3 ft deep: - V = 4 × 2 × 3 = 24 cubic feet = 179.5 gallons
Horizontal Cylindrical Tank Volume
Fuel tanks, propane storage, and many industrial tanks lie on their sides.
Full volume: V = π × r² × L (same as vertical, using length instead of height)
Partial fill (liquid depth d): More complex — requires the cross-sectional area of a circular segment:
V = L × [r² × arccos((r−d)/r) − (r−d) × √(2rd − d²)]
For practical use: Most users reference a horizontal cylinder fill table or use a calculator that handles this formula.
Quick estimates for horizontal tanks: - 25% full (d = 0.5r): 19.4% of total volume - 50% full (d = r): 50% of total volume (exact half) - 75% full (d = 1.5r): 80.6% of total volume
Cone Tank Volume (Hopper Bottoms)
Grain bins and agricultural hoppers often have conical bottoms.
For conical section: V_cone = (1/3) × π × r² × h For cylindrical section above cone: V_cyl = π × r² × h_cyl Total = V_cone + V_cyl
Spherical Tank Volume
Large liquid petroleum gas (LPG) storage spheres.
Formula: V = (4/3) × π × r³
Example: 10-foot diameter sphere: - r = 5 ft - V = (4/3) × π × 125 = 523.6 cubic feet = 3,917 gallons
Unit Conversions
Common Tank Size Reference
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Frequently Asked Questions
- How do you calculate the volume of a cylindrical tank?
- V = π × r² × h, where r is the radius (diameter ÷ 2) and h is the height. For a tank with 4-foot diameter and 5-foot height: r = 2, V = π × 4 × 5 = 62.83 cubic feet. To convert to gallons, multiply by 7.48 = 470 gallons.
- How do I calculate how many gallons a rectangular tank holds?
- Volume (cubic feet) = Length × Width × Height. Then multiply by 7.48 to convert to US gallons. A 6 ft × 4 ft × 3 ft tank: V = 72 cubic feet × 7.48 = 538 gallons. For measurements in inches, divide the result by 231 (cubic inches per gallon).
- How do you calculate volume of a horizontal cylinder tank when partially filled?
- The exact formula uses circular segment area: V = L × [r² × arccos((r−d)/r) − (r−d) × √(2rd − d²)], where d is liquid depth and r is radius. For common fill levels: at 50% depth, exactly 50% volume; at 25% depth, ~19.4% of total volume; at 75% depth, ~80.6% of total volume.
- How many gallons are in a cubic foot?
- 1 cubic foot = 7.48052 US gallons. This is the most important conversion for tank volume calculation. For liters: 1 cubic foot = 28.317 liters. For Imperial gallons (UK): 1 cubic foot = 6.229 Imperial gallons.
Last updated 7/28/2026