How can I find or calculate the size of my water heater tank?

A split heat pump water heater is shown with a storage tank and heat pump unit.

Determining the size of your current water heater:

1. Check the Label

Look for a label or nameplate on the side of your water heater. This label typically includes the tank's capacity, listed in gallons. You should see terms like "Capacity," "Nom. Cap" as well as "Gallons," or "Gals" on this label.

2. Measure the Dimensions

If the label is not available, you can measure the tank's dimensions:

• Height: Measure from the base of the heater to the top.
• Diameter: Measure across the widest part of the tank.

Now you'll need to brush up on your high school geometry.

The formula for the volume of a cylinder is: 𝑉=𝜋𝑟²h

Where:

• V is volume
• π (pi) is approximately 3.14159
• r is the radius of the base
• h is the height of the cylinder

Example Calculation

Let's say you have a water heater with the following dimensions:

• Diameter: 20 inches
• Height: 48 inches

1. Calculate the radius: 20 inches ÷ 2 = 10 inches
2. Apply the formula:
   𝑉=3.14159 × 10² × 48 = 15,079.63 cubic inches
3. Convert to gallons:
   15,079.63 cubic inches ÷ 231 (cubic inches per gallon) = 65.28 gallons

So this water heater would have a capacity of approximately 65 gallons.