- Calculate the size or water holding capacity of a square or rectangular water tank by measuring the length, width and depth of the tank in feet. Multiply the length by the width and the depth to calculate the cubic feet. Multiply the cubic feet by 7.47 to determine the capacity of the tank in gallons.
- Determine the size or water holding capacity of a round, flat-bottom tank by measuring the radius and depth. The radius is one-half of the diameter. Multiply 3.1417 by the radius squared by the depth to calculate the cubic feet. The tank capacity in gallons is obtained by multiplying the cubic feet by 7.47.
- Calculate the water holding capacity of a cylindrical tank by multiplying the square area of the base by the height of the tank. To determine the square area of the base, measure the diameter of the tank in feet. Multiply the diameter squared by .7854. Then multiply the square area of the base by the height of the tank in feet. Multiply the value by 7.47 to determine the capacity in gallons.
- Utilize a water tank that delivers the desired number gallons of water per minute, hour or day. The size and design of the water tank must provide adequate water pressure. Tanks may be permanent or portable and are available in a huge array of sizes and shapes.

# How to Size Water Tanks

Polyethylene, steel, concrete and fiberglass are common materials used to construct water tanks. A water tank is any container designed to hold liquids. Ground water tanks sit on the ground. A lack of water pressure is a major disadvantage of ground water tanks and water often has to be pumped. Elevated water tanks are on legs above the ground and continuous pumping is usually not required. The capacity of a water tank is the volume of water it can hold.