To determine how many chemicals to add to a tank, or to determine if it’s a time for a refill, it’s important to understand how to measure water in tanks. The water tank volume refers to how much space the water takes up in your three-dimensional water tank. When you measure water tanks, take your measurement in inches to maintain consistent numbers throughout your calculation. If possible, measure the inside of the tank for the most accurate water tank measurements.

### Things You'll Need

- Tape measure
- Paper
- Pencil

- Calculator
- Long piece of wood

Measure the length of your water tank. Run your tape measure from one end of your water tank to the other. Write down your measurement.

Determine the height of your water tank by measuring from the bottom of the tank to the top.

Calculate the depth of your water tank by measuring from the front of your water tank to the back. You can usually take this measurement best on the side of the water tank.

Multiply the length times the height times the depth. Multiply that result by 0.00433. Your formula is “water tank volume = length x height x depth x 0.00433.” The number you obtain as a result of this formula will tell you how many gallons of water your tank holds.

Run your tape measure from the bottom of the tank to the top of the water line to calculate how much water is in your tank. If you can’t see the water line, lower a piece of wood or any other long object into the tank until it reaches the bottom. Pull it back out and measure the length of wood, stopping where you can see the water line.

Figure out how much water you have in your tank by multiplying the length and depth you calculated previously by your new height, which reflects the measurement from the bottom of the tank to your water line. Multiply that result by 0.00433 to determine how many gallons of water are in your tank.

Subtract the amount of water in your tank from the amount of water your tank can hold to determine how much water you need to add to your water tank.