How do I know if I have a 2-inch or 3-inch flush valve?

To determine your flush valve size, use one (or more) of the 5 simple methods below. 2-inch openings typically measure 1.8–2.3 inches, while 3-inch openings measure 2.8–3.2 inches. You can also check the flapper size, molded markings, or toilet model specifications for confirmation.

5 Simple Ways to Check Flush Valve Size

1. Measure the Tank Drain Opening (Most Accurate)

• Remove the tank lid and turn off the water supply to avoid spills

• Use a ruler or measuring tape to measure the inner diameter of the circular opening at the tank bottom (where the flush valve attaches)

• 2-inch: 1.8–2.3 inches; 3-inch: 2.8–3.2 inches

• If the tank is in the way, remove it to measure the ceramic drain hole directly

2. Check the Flapper (Quick Visual/Measurement)

• For flapper-style valves: Measure the flapper’s width (end to end)

• 2-inch valve → flapper ~3 inches wide; 3-inch valve → flapper ~4 inches wide

• For tower/canister-style valves: Measure the base diameter of the tower (matches the valve size)

3. Look for Molded Markings

• Check the flush valve body, flapper, or tank for stamped/molded “2” or “3” (common on Fluidmaster, Toto, Kohler, etc.)

• If no marking, proceed to measure

4. Visual Comparison (Rough Estimate)

• 2-inch: ~size of a baseball/orange

• 3-inch: ~size of a softball/grapefruit

• This is a backup; always measure for certainty

5. Check Toilet Model/Manufacturer Specs

• Find the model number on the toilet tank (inside back or underside) or base

• Look up the specs online or contact the manufacturer—many post flush valve sizes for their models

• Note: Pre-2005 toilets are often 2-inch; post-2005 low-flow models may use 3-inch for better flushing efficiency

Size Guide at a Glance

Pro Tips

• Turn off the water and flush to empty the tank before measuring for safety

• If replacing parts, match the valve size to the flapper/tower seal to prevent leaks and ensure proper flushing

• Universal 2-inch flappers fit most 2-inch valves; 3-inch valves need 3-inch flappers for a tight seal