Tank Volume Calculator

How to Calculate Tank Volume?

Tank volume depends on the tank shape and dimensions. For rectangular tanks, multiply length x width x depth. For vertical cylindrical tanks, use pi x radius squared x height. For horizontal cylindrical tanks, the same formula applies (pi x radius squared x length). The calculator above supports all three configurations and converts the result into cubic feet, US gallons, liters, and barrels. Enter your tank dimensions in feet to find the total capacity in all common volume units instantly.

How to Calculate Rectangular Tank Volume?

Multiply the inside length, width, and depth in feet. A tank 6 x 4 x 3 feet holds 72 cubic feet. Multiply by 7.48 for US gallons: 72 x 7.48 = 538.6 gallons. Multiply by 28.317 for liters: 72 x 28.317 = 2,038.8 liters. If dimensions are in inches, multiply all three and divide by 231 to get gallons directly (231 cubic inches per gallon). Rectangular tanks are used for water storage, fish tanks, industrial processing, and rainwater collection systems. Wall thickness is not included in the volume calculation because the inside dimensions represent the actual water-holding space.

How to Calculate Cylindrical Tank Volume?

For vertical cylinders (standing upright): volume = pi x radius squared x height. A vertical tank 4 feet in diameter and 6 feet tall: radius = 2 feet, volume = 3.14159 x 4 x 6 = 75.4 cubic feet = 564 gallons. For horizontal cylinders (lying on their side): the same formula applies, but "height" is replaced by "length." A horizontal tank 3 feet in diameter and 8 feet long: radius = 1.5, volume = 3.14159 x 2.25 x 8 = 56.5 cubic feet = 423 gallons. Horizontal tanks are common for propane, fuel oil, and underground water storage because their low profile distributes weight evenly and fits in constrained vertical spaces.

Common Tank Sizes and Capacities

Residential hot water heater: 40-80 gallons. Septic tank: 1,000-1,500 gallons. Residential propane tank: 120-500 gallons (above ground) or 500-1,000 gallons (underground). Residential rainwater collection: 50-2,500 gallons. Agricultural water tank: 1,000-10,000 gallons. Residential oil tank: 275 gallons (standard basement tank). Swimming pool: 10,000-30,000 gallons. Fire suppression cistern: 10,000-30,000 gallons. Industrial storage tanks range from a few hundred to millions of gallons depending on the application and industry.

Why Does Knowing Tank Volume Matter?

Tank volume determines fill quantity, chemical dosing, pump sizing, and structural support requirements. A water tank holding 1,000 gallons weighs approximately 8,340 pounds when full (water weighs 8.34 lbs per gallon). The foundation or support structure must carry this weight. Fill time depends on volume and flow rate: a 1,000-gallon tank at 10 GPM takes 100 minutes to fill. Chemical treatment of stored water requires dosing based on the exact volume. Heating a tank of water requires 8.34 BTU per gallon per degree Fahrenheit of temperature rise. Every one of these calculations starts with an accurate volume figure.

How to Convert Between Volume Units?

1 cubic foot = 7.481 US gallons = 28.317 liters. 1 US gallon = 3.785 liters = 0.1337 cubic feet. 1 barrel (oil industry) = 42 US gallons. 1 barrel (other industries) = 31.5 US gallons. 1 cubic meter = 264.2 US gallons = 35.31 cubic feet. 1 imperial gallon = 1.201 US gallons. When reading tank specifications from different countries, verify whether "gallon" means US gallon or imperial gallon, as the 20% difference causes significant volume errors in large tanks. The calculator uses US gallons as the standard unit.

Partial Fill Volume for Horizontal Cylinders

Calculating the volume of a partially filled horizontal cylinder is more complex than a full cylinder. When a horizontal tank is not completely full, the liquid forms a segment shape that requires the formula: volume = length x (radius squared x arccos((radius - depth)/radius) - (radius - depth) x sqrt(2 x radius x depth - depth squared)). Most people use a tank volume chart or calculator rather than this formula. Knowing the partial fill volume is important for fuel tanks and process tanks where you need to track how much liquid remains. Many tanks have a sight glass or float gauge that indicates the fill level, but converting that level reading to actual gallons requires the partial fill calculation for the specific tank dimensions.

Tank Material and Application Considerations

Polyethylene tanks are lightweight, corrosion-proof, and the most common choice for above-ground water storage (100-10,000 gallons). Fiberglass tanks resist chemicals and are used for underground water and fuel storage. Steel tanks are the standard for propane, industrial fuel, and high-pressure applications. Concrete tanks are used for septic systems and large underground cisterns. Stainless steel serves food-grade and pharmaceutical applications. The tank material does not affect volume calculations but determines the wall thickness, which affects the difference between outside dimensions and inside (usable) dimensions. Always use inside dimensions for volume calculation.

Frequently asked questions