What size rubber washer for toilet tank?
Toilet tank rubber washer sizes vary by type (bolt, flush valve shank, tank-to-bowl), with the most common sizes for 2-inch flush valves and 5/16-inch tank-to-bowl bolts being standard in residential toilets.
Common Sizes by Type
| Washer Type | Key Sizes (Imperial/Metric) | Typical Use |
|---|---|---|
| Tank-to-Bowl Bolt Washer | 5/16" bolt fit (ID ~0.31", OD ~1.06", height ~0.28"); M6 (ID 6mm, OD 25mm) or M8 (ID 8mm, OD 27mm) conical washers | Under tank bolt nuts to stop leaks between tank and bowl |
| Flush Valve Shank Washer | ID 2.35–3.5", OD 3.15–3.5", thickness 0.36" | Between tank interior and flush valve base |
| Tank-to-Bowl Gasket (Sponge Rubber) | 2-inch flush valve: ID 2-1/8"–2-1/4", OD 3-1/16"–3-5/16" 3-inch flush valve: ID 3", OD 4-1/4" | Main seal between tank outlet and bowl inlet |
How to Confirm the Right Size
Check the toilet model number (usually inside the tank) and consult the manufacturer’s specs.
Measure the old washer’s ID, OD, and thickness with a caliper or ruler.
For flush valves, measure the valve shank diameter to match the washer ID.
For bolts, confirm the bolt diameter (most are 5/16") to get the correct bolt washer ID.
Sizing Tips
Most residential toilets use 2-inch flush valves, so a 2-inch tank-to-bowl gasket is standard.
3-inch flush valves are common in newer high-efficiency toilets; match with a 3-inch gasket.
Universal kits often include 5/16" bolt washers and 2-inch gaskets, which fit most toilets.
Need me to help you measure your old washer/gasket with a simple step-by-step guide and confirm the exact size?
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