Quick Answer
Measure the distance from the centre of the two seat bolt holes to the front rim of the bowl: 16.5 inches is a standard round seat, 18.5 inches is elongated. Buy the matching shape.
Pop the plastic caps at the back of the existing seat, unscrew the bolts (hold the nut underneath if needed), lift the old seat off, and clean the porcelain. Drop the new seat in, push the bolts through the hinges, and tighten the self snapping nuts from below until the collars break off.
The whole job takes about 15 minutes and needs only a screwdriver or small adjustable wrench.
Tools and parts
- Tape measure.
- Flathead screwdriver to pop the bolt caps.
- Phillips screwdriver or small adjustable wrench.
- Rubber gloves.
- Disinfectant spray and a cloth.
- A new toilet seat (round or elongated) with its hardware included.
Most modern seats ship with self snapping nylon bolts that need no separate wrench. Older two piece sets may need a deep socket or a basin wrench if the nut sits inside a recess.
Measure round versus elongated
The only measurement that matters is the bowl length:
- Round: 16.5 inches from the centre of the bolt holes to the front of the bowl.
- Elongated: 18.5 inches.
If you measure something in between, round to the nearest of the two. Bolt hole spacing is standardised at 5.5 inches across virtually every modern toilet, so you do not need to measure that.
Remove the old seat
Put on gloves and lift the seat. Look at the two hinges at the back. Each one has a small plastic cap covering the bolt head. Slide a flathead screwdriver under the rear lip of the cap and lever it up. Some caps flip open instead of popping off.
Reach under the rear of the bowl and grip the plastic nut on the bottom of the bolt with your fingers. With your other hand, turn the bolt head counterclockwise with the screwdriver. The nut will spin off, or the bolt will lift straight out.
If the nut is corroded or spinning with the bolt, hold it steady with a small wrench or pair of pliers and keep turning the top. As a last resort, cut the bolt with a hacksaw, wrapping the porcelain in tape first to protect it.
Lift the old seat away and spray the exposed porcelain with disinfectant. Wipe it dry.
Install the new seat
- Set the new seat on the bowl so the hinge bolt slots line up directly over the porcelain holes.
- Drop the rubber washers (if separate) flat onto the porcelain, then push the new bolts down through the hinges and the washers.
- From below, thread the plastic nut up onto each bolt by hand until it sits snug against the underside of the rim.
- Snug each nut with a wrench or screwdriver. Modern self snapping nuts have a sacrificial collar that breaks off with an audible click when the correct torque is reached, preventing overtightening.
- Open and close the seat to confirm it does not wobble. If it shifts, you can usually adjust by loosening the bolts a quarter turn, sliding the seat square, and retightening.
- Snap the decorative caps back down over the bolt heads.
Soft close versus standard
Soft close seats use a damped hinge that lowers the lid and ring slowly. They cost a few dollars more but eliminate the slamming noise and last longer than basic plastic hinges because the lid never crashes against the bowl.
The installation is identical. Some soft close models include a quick release button on the hinge that lets you lift the whole seat off in seconds for deep cleaning.
Common problems and fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Seat still wobbles | Bolts not fully tightened or seat not square | Loosen, recentre, retighten |
| Bolts will not turn | Corroded or seized hardware | Spray penetrating oil, wait 15 min, retry |
| Hairline crack near bolt hole | Overtightened nut | Replace seat with new bolts, finger tight plus a quarter turn |
| Bolt spins with nut | Plastic bolt head stripped | Hold nut with pliers, cut bolt if needed |
How long a toilet seat lasts
Plastic seats last about 5 to 7 years before the hinges wear out. Enameled wood seats can last a decade if dried after every clean. The hardware almost always fails before the seat itself, so a wobbly seat is usually a 5 minute bolt swap rather than a full replacement.
Frequently asked questions
How do I know if my toilet is round or elongated?
Measure from the bolt holes at the back to the front rim. 16.5 inches is round, 18.5 inches is elongated.
Are all toilet seat bolts the same size?
The hole spacing is universal at 5.5 inches centre to centre, but bolt length and material vary. Most replacement seats ship with their own bolts.
Can I install a toilet seat without a wrench?
Yes. Modern self snapping nuts tighten by hand or with a screwdriver and break off at the correct torque.
How tight should toilet seat bolts be?
Tight enough that the seat does not shift when you press down, but not so tight that the porcelain creaks. Self snapping collars stop you at the right point automatically.
