Tank Volume Calculator
Calculate the volume of rectangular, cylindrical, and spherical tanks in gallons and liters. See also Pipe Volume Calculator, Pool Volume Calculator, and Cubic Yard Calculator.
Tank Shape
How to Use the Tank Volume Calculator
Select your tank shape — rectangular, vertical cylinder, horizontal cylinder, or spherical. Enter the dimensions in feet. For partial fill calculations, enter the current liquid level in the fill level field. The calculator determines total capacity and current volume in gallons, liters, and cubic feet. Horizontal cylinder fill calculations use the circular segment formula for accurate partial-fill volumes.
Formula
Rectangular: V = L x W x H
Cylinder: V = PI x r² x H
Sphere: V = (4/3) x PI x r³
Gallons = Cubic Feet x 7.48052
Liters = Gallons x 3.78541
Example Calculation
Vertical cylinder: 4 ft diameter, 3 ft tall
Volume = PI x 2² x 3 = 37.70 cu ft
Gallons = 37.70 x 7.48 = 282.0 gallons
Liters = 282.0 x 3.785 = 1,067.4 liters
Standard Tank Sizes Reference
| Tank Type | Dimensions | Gallons | Common Use |
|---|---|---|---|
| Residential water heater | 20" dia x 48" tall | 40-50 | Hot water storage |
| Propane (vertical) | 24" dia x 48" tall | 100 | Residential heating |
| Septic tank | 5 x 8 x 4 ft | 1,000 | Wastewater |
| Rain barrel | 24" dia x 36" tall | 55 | Rainwater collection |
| IBC tote | 4 x 4 x 4 ft | 275 | Industrial storage |
| Underground fuel | 4 ft dia x 8 ft | 500 | Fuel storage |
Frequently Asked Questions
How do I measure a horizontal cylindrical tank's fill level?
Measure the liquid depth from the bottom of the tank to the surface. For horizontal cylinders, the volume is not linear with depth — a tank half full by height contains exactly 50% of its volume, but at 25% height it holds only about 15% of total volume due to the circular cross-section.
How many gallons are in a cubic foot?
One cubic foot equals 7.48052 US gallons. This conversion factor is essential for tank volume calculations. For reference, one cubic meter equals 264.172 US gallons.
What size water tank do I need for my home?
Average household water usage is 80-100 gallons per person per day. For emergency storage, plan 1 gallon per person per day minimum. A family of 4 needs at least a 500-gallon tank for 3-day emergency supply or a 2,500-gallon tank for rainwater harvesting.
How do I calculate the weight of water in my tank?
Water weighs 8.34 pounds per gallon (62.4 lbs per cubic foot). Multiply your tank's gallon capacity by 8.34 to get the water weight. A full 500-gallon tank weighs approximately 4,170 pounds — ensure your support structure can handle this load.
What is the difference between nominal and actual tank capacity?
Nominal capacity is the manufacturer's rated size. Actual usable capacity is typically 80-90% of nominal because tanks should not be filled completely (thermal expansion, overflow prevention). A "500-gallon" tank may only safely hold 400-450 gallons.
How long does it take to fill a tank?
Fill time = Tank volume (gallons) / Flow rate (GPM). A standard garden hose delivers 5-10 GPM. A 500-gallon tank takes 50-100 minutes to fill with a garden hose. Municipal water supply at 15-20 GPM fills the same tank in 25-33 minutes.