How to Measure the Flow Rate of a Toilet

Updated February 21, 2017

Since water is a non-renewable resource, water conservancy is an important issue for the planet. Measuring the flow rate of your toilet can help you determine if your home is wasting too much water, and can help you decide whether you should replace your toilet with a more efficient, water-conserving model. The term "flush volume" refers to how much water the toilet uses for each flush. While high efficiency toilets may use as little as 1.28 gallons per flush, the Marin Municipal Water District of Marin County, California, suggests replacing your toilet if it has a flush rate of 3.5 gpf or more.

Turn off the water supply behind the toilet by turning the valve to the right.

Remove the tank lid from the toilet and set aside.

Mark the water level inside the both the toilet tank and toilet bowl with a small piece of masking tape.

Flush the toilet until it doesn't fill up with water any more.

Fill a 1-gallon container or bucket with water, and pour the water into the tank until you reach the masking tape line. Refill the container as needed, and keep track of how much water it took to fill the tank to the masking tape line.

Fill the toilet bowl until the water reaches the masking tape line, and keep track of how much water it took to fill the bowl.

Add together the number of gallons it took to fill the tank and the bowl together to determine your gpf rate.

Replace the water tank lid, and turn the water supply on by twisting the valve to the left.


Check the label behind the seat hinge on the bowl for a manufactured date, or a stamped date on the porcelain. Toilets before 1982 commonly use 5 to 7 gpf, toilets between 1982 and 1990 commonly use 3.5 gpf, toilets between 1990 to 1992 commonly use 1.6 to 3.5 gpf, toilets between 1994 to 2005 commonly use 1.6 gpf and toilets between 2005 to 2011 commonly use 1.28 gpf, notes the Marin Municipal Water District.

Things You'll Need

  • Masking tape
  • 1-gallon bucket or container
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About the Author

Lauren Thomason has written professionally since 2011 for online publications such as eHow. She is an avid gardener and crafter, history buff and science experiment fanatic. She holds a Master of Science in elementary education and is pursuing a Doctor of Education from Liberty University.