Illustration showing the rotation of the handle dial when measuring gallons per flushToilets that Use More Water

When you flush your toilet, you probably don’t usually think about how much water is being used, right? Well, believe it or not, it is very possible that toilets in your home/business are flushing over a gallon of water every time you flush. That amount of water usage can add up very quickly. Most standard toilets can range from 1.6 to 3.5 gallons of water, depending on the age and type of toilet you have.

Many cities are now requiring California residents to have toilets that flush less than 1.6 gallons per flush. This will usually require a high-efficiency toilet replacement.

Flush Volume

To find the amount of water that your toilet uses, there are three main methods:

1. Look on the base of the toilet, where the bowl and tank meet. Sometimes there is a stamp there with the toilet brand name and the gallons per flush (GPF).
2. Open up the toilet tank lid and look inside the toilet tank to see if there’s anything written/stamped into the inside of the tank.
3. Look on the underside of the toilet tank lid. There might be some information there, including GPF.

If there are no markings, chances are your toilet is flushing over 1.6 GPF.

If you still want to know how much your toilet is flushing, there are two other methods you can try:

Close up of a water supply valve coming from the wall and connecting to the toilet

Toilet Tank Capacity Method

Turn off the water supply valve to the toilet.
Remove the tank lid, look for the water line on the inside back wall of the tank, if there’s no line, mark it with a pen/pencil.
Flush the toilet.
Fill the tank with water up to the line inside the tank (or the one you drew). Note how many gallons it took to fill the tank back up. Add ½ gallon to that number. That’s how many gallons your toilet uses.
Turn on the water supply valve when you are finished.

Illustration showing the rotation of the handle dial when measuring gallons per flush

Water Meter Method

Turn off all fixtures that are using water in your home/business. Locate the water meter.
Remove the meter’s lid, note the location of the red dial hand.
Flush the toilet one time. Once the toilet has finished refilling, read the meter and see how far the red dial hand has moved. Each full rotation of the dial hand is equal to one cubic foot or 7.5 gallons of water.

Rotation of Dial Hand

less than ¼: 1.6 GPF
about ½: 3.5 GPF
about ⅔: 5.0 GPF
full rotation: 7.0 GPF

The newer water meters have no dial hand, but you can still use this method.
Read the last two digits to the right of the decimal point.
Read again. Subtract the first reading from the second and multiply the result by 7.5 to get gallons per flush.