Key takeaways
- Most bathroom sink drains measure 1.25 inches across the opening; a minority are 1.5.
- Kitchen sinks use a 3.5 inch basket strainer, which is a different fitting entirely.
- Measure the inside of the drain opening, not the trim ring or the pipe below.
- Too small a stopper wobbles and will not seal; too large never reaches the seat.
- Some replacements include seals for both sizes - the seal changes the effective diameter.
Most bathroom sink drains in North America are 1.25 inches across the opening. A minority are 1.5 inches. Kitchen sinks are not either of those - they use a 3.5 inch basket strainer, which is a different fitting entirely. And that is the whole source of the confusion: three numbers, two of which sound like the same thing when you are standing in a store holding a stopper.
The two sizes, in one line
If you only remember one thing: measure the inside of the drain opening, and most bathroom sinks will come out at 1.25 inches. If yours is 1.5, you have one of the less common basins - and if you are measuring a kitchen sink and getting 3.5, you are not looking for a stopper at all.
Where each size shows up
The 1.25 inch drain is the standard bathroom basin drain, and it is what most pop-up stoppers and most replacement plugs are made for. The 1.5 inch drain appears on some bathroom sinks - often older ones, or specific brands - and it is also the common bathtub drain size, which is exactly why a 1.5 inch sink stopper and a 1.5 inch tub stopper are still not the same part. The 3.5 inch figure belongs to kitchen basket strainers: those are the wide baskets with a handle or a plug, not a pop-up stopper. In the UK and Europe, wastes are measured in millimetres - a 32 mm basin waste is roughly the same job as the 1.25 inch drain, and 40 mm corresponds to the larger sizes.
| Size | Where it is used | What fits |
|---|---|---|
| 1.25 inch | Most bathroom sink drains (US/CA) | Pop-up stoppers, most replacement plugs |
| 1.5 inch | Some bathroom sinks; bathtub drains | Larger pop-up stoppers; tub stoppers (different fitting) |
| 3.5 inch | Kitchen sinks | Basket strainers, not stoppers |
| 32 / 40 mm | UK and EU basin and kitchen wastes | Metric-size wastes and stoppers |
How to measure yours in two minutes
Pull the stopper out first - on most pop-up drains it lifts straight up, and if it will not, loosen the pivot rod nut underneath and slide the rod back. What you are measuring is the round opening in the drain body: the inside diameter of the hole, not the decorative ring around it and not the pipe below. A ruler laid across the opening is accurate enough for this job, because the difference between the two sizes is a quarter of an inch - a gap you can see. Measure twice, at right angles, in case the opening is slightly oval from wear.
If the opening is awkward to reach, our step-by-step guide to sink drain stopper sizes shows exactly where to put the ruler - and if the sink is not sealing either, start with five fixes for a leaking pop-up drain.
What happens if you buy the wrong size
A stopper that is too small is the more common mistake, and it behaves predictably: it drops deep into the drain, wobbles, and will not seal, so the sink holds no water at all. A stopper that is too large sits proud of the drain, never reaches the seat at the bottom, and also will not seal - it just looks wrong, which is at least easier to diagnose. In both cases the sink will either not hold water or drain slowly while you assume the drain is blocked.
If you already bought the wrong one
Return it if you can, because nothing about a stopper is adjustable. The one thing worth knowing is that some replacements ship with seals for both sizes: the seal changes the effective diameter, so the same stopper body can be made to fit a 1.25 or a 1.5 inch drain if the seal is right. That is why the packaging lists both. But the stopper body itself still has to match the opening - a seal cannot stretch a 1.25 inch stopper into a 1.5 inch hole. If you are replacing the whole drain rather than the stopper, measure the tailpipe thread and the sink thickness as well, because those come into it at that point.
The bottom line
One number answers all of it: the inside diameter of the drain opening. Most bathroom sinks measure 1.25 inches, a minority measure 1.5, kitchen sinks use a 3.5 inch basket strainer, and tub drains - also around 1.5 - are a different fitting despite the matching number. Measure before you buy, and if the old stopper came with two seals, you will find out why on the first try.
Frequently asked questions
How do I know if my sink drain is 1.25 or 1.5 inches?
Pull the stopper and measure the inside of the drain opening with a ruler or calipers. Most bathroom sink drains measure 1.25 inches; a minority measure 1.5.
What happens if my sink stopper is too small?
It drops deep into the drain, wobbles and will not seal, so the sink holds no water at all. Too large is the opposite: the stopper sits proud and never reaches the seat.
Is a kitchen sink drain 1.5 inches?
No - kitchen sinks almost always use a 3.5 inch basket strainer, which is a different fitting. The 1.25 and 1.5 inch sizes are for bathroom basin drains and tub drains.
Can one stopper fit both 1.25 and 1.5 inch drains?
Some replacements include seals for both sizes, which changes the effective diameter. The stopper body still has to match the opening - a seal cannot stretch a 1.25 inch stopper into a 1.5 inch hole.
Related reading
- Sink drain stopper sizes: how to measure yours correctly
- Bathtub drain stopper sizes and types (and why sink stoppers don't fit)
- Sink stopper won't hold water? 5 fixes for a leaking pop-up drain
If the parts above the drain are what you are replacing, the one we make is our pop-up sink drain stopper - the basket lifts out, so cleaning it is a ten-second job.