QUESTIONS
Can a top fix toilet seat replace a bottom fix toilet seat?
Updated 07/26
By: Alex Peters
Reviewed: Content Team
Usually yes, but not the other way round. If your toilet currently has a bottom fix seat, you can generally switch to a top fix seat instead, as long as the fixing holes and dimensions match. But if your toilet only has top fix (blind hole) fixings, a bottom fix seat won't work at all, since there's nothing to reach or tighten from underneath.
Here's how to tell which you have, and what else needs to match before you buy a replacement.
Whether you can switch from bottom fix to top fix
How to identify which fixing type your toilet has
The measurements that matter more than the fixing type
Why some replacements won't fit even with the right fixing
Roughly what professional fitting costs
When it's worth calling a plumber instead of DIY
Find a plumber near me
What's the difference between top fix and bottom fix?
Bottom fix: a bolt drops through the fixing hole from above and is tightened from underneath the pan, usually with a wing nut. You need to be able to reach and access the underside of the pan for this to work.
Top fix: the fitting is inserted into the hole and tightened entirely from above, often using an expanding fixing that grips inside the ceramic. No access underneath is needed.
Top fix has become the default on most modern toilets because it's easier to fit and remove for cleaning, and because many modern designs (back-to-wall toilets, wall-hung toilets, and closed-back close-coupled toilets) fully enclose the base, leaving no way to reach underneath at all.
To check which you have, reach behind and underneath the toilet bowl at the fixing holes. If you can feel a bolt and a nut, it's bottom fix. If the underside is smooth and fully enclosed with no access, it's top fix only.
Can I replace a bottom fix seat with a top fix one?
Generally, yes. If your toilet has open access underneath (a bottom fix toilet), you can usually fit a top fix seat instead if you'd prefer, since you're simply choosing not to use the underneath access rather than needing it. Some people prefer this, since it avoids lying on the bathroom floor to fit or remove the seat.
The reverse doesn't work: if your toilet is enclosed with blind hole, top-fix-only fixings, a bottom fix seat has nothing to bolt onto from underneath, and simply won't fit no matter how well everything else matches.
The measurements that matter just as much as fixing type
Getting the fixing type right is only part of it. Before buying a replacement seat, measure:
Fixing hole distance - centre-to-centre distance between the two fixing holes. Many UK toilets use a standard spacing (often around 155mm), but this varies by brand and model, so always check rather than assume.
Seat length - measured from the centre of the fixing holes to the front edge of the pan.
Pan width - the widest point of the bowl, measured outer edge to outer edge.
Most replacement seats have some adjustment built into the hinges, but if your measurements fall outside that adjustable range, the seat won't sit correctly even with the right fixing type.
Remove your old seat before measuring. It's much easier to get accurate figures directly from the pan than trying to measure around an existing seat.
Toilet seat shape matters too, alongside fixing type and measurements. Round, D-shaped, and square pans aren't interchangeable, so check your toilet's shape against the seat you're buying, not just the brand name. If you're dealing with a wider toilet issue rather than just the seat, our guide to concealed cistern problems covers related fixes.
Do I need a plumber to fit a toilet seat?
Fitting a toilet seat is one of the more DIY-friendly bathroom jobs, and plenty of people do it themselves with basic tools. That said, it's worth getting a professional in if:
The old fittings are corroded, seized, or won't budge without risking damage to the pan
You're not confident identifying the fixing type or taking accurate measurements
You want the toilet seat fitted as part of a wider bathroom job
On Checkatrade, you'll only find trades who meet our high standards and pass up to 12 checks.
Hire an experienced local tradesperson
If you'd rather have it done properly first time, or you're dealing with a wider toilet issue alongside the seat, Checkatrade can help you find local, vetted plumbers and toilet specialists.
Toilet installation cost in the UK in 2026
Wondering how much it costs to install or replace a toilet? Explore toilet installation costs, plumber rates, replacement prices and fitting costs.
Before you buy a replacement seat
Frequently asked questions
Only if your toilet has accessible fixing holes to bolt into, whether that access is from above or underneath. A fully enclosed pan with only blind-hole top fixings needs a top fix seat specifically designed for that fixing.
No. If there's no way to reach underneath the pan, a bottom fix seat has nothing to tighten onto and won't work.
Remove the existing seat and measure centre-to-centre between the two fixing holes. Many UK toilets use a similar standard spacing, but always measure rather than assume, especially with modern or designer pans.
No. Fixing type, hole distance, seat length, pan width, and pan shape all need to match (or fall within the seat's adjustable range) for a proper fit.
Usually a mismatch in fixing hole distance or seat length rather than a fixing type problem. Double-check your measurements against the new seat's specification before assuming it's faulty.
If you're already replacing the seat, it's a reasonable moment to upgrade, since the cost difference is usually small and both are widely available in top fix and bottom fix versions.
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