Sink Drain Size Guide: Kitchen and Bathroom Sizes

Short answer

Bathroom sink drains are 1-1/4 inch pipe; kitchen sink drains are 1-1/2 inch pipe. The hole in the sink is a separate measurement: about 3-1/2 inches in most US kitchen sinks, and roughly 1-1/4 to 1-3/4 inches in bathroom sinks, where there is no single standard. Measure the hole with the old drain out and buy to the range on the box.

Measure your drain hole

The size chart

Sink drain sizes at a glance

Part	Typical size	What to know	Source
Bathroom sink tailpiece	1-1/4 in	The pipe under a bathroom (lavatory) sink drain. Its P-trap is 1-1/4 in too.	Source
Kitchen sink tailpiece	1-1/2 in	The pipe under a kitchen basket strainer or disposal. Its P-trap is 1-1/2 in.	Source
Kitchen sink drain hole	3-1/2 in	The usual US kitchen opening. Some strainers are made to cover 3-1/2 to 4 in.	Source
Bathroom sink drain hole	About 1-1/4 to 1-3/4 in	There is no single standard. Measure the hole and match the range on the drain box.	Source
P-trap water seal	2 to 4 in deep	The International Plumbing Code calls for a seal of at least 2 in and no more than 4 in.	Source
Vessel sink drain	Bowl hole plus counter	Usually no overflow. Needs a body long enough for the bowl and counter together.	Source

Fig. 2 The parts that carry a size: the strainer or pop-up sits in the hole; the tailpiece and trap carry the pipe size.

How to measure without guessing

Hole: with the old drain out, measure straight across the hole in the sink, edge to edge. The flange on top is always wider than the hole, so measuring it gives the wrong answer.
Pipe: wrap a strip of paper around the tailpiece, mark where it overlaps, and measure the length. About 4 inches around is 1-1/4 inch pipe; about 4-3/4 inches around is 1-1/2 inch pipe.
Thickness: measure the sink (plus the counter, for a vessel bowl) at the hole. Compare it with the maximum thickness on the drain listing.

When the sizes do not match

1-1/4 inch drain onto a 1-1/2 inch trap: use a reducing slip washer or a 1-1/2 by 1-1/4 inch adapter. Reducing washers on Amazon.
Kitchen hole larger than 3-1/2 inches: look for strainers made to cover 3-1/2 to 4 inch openings, like the Keeney clip closure.
Bathroom hole outside the usual range: take the old drain with you to a plumbing supply store.

The trap and its water seal

Every trap under a sink holds water to block sewer gas. The International Plumbing Code calls for a seal at least 2 inches and no more than 4 inches deep (ICC). Bathroom traps match the 1-1/4 inch tailpiece; kitchen traps are 1-1/2 inch. More in the P-trap guide.

See P-trap kits

Questions people ask

Are all bathroom sink drains the same size?

The pipe is: bathroom drains use a 1-1/4 inch tailpiece. The hole in the sink is not. Bathroom sink holes vary, roughly 1-1/4 to 1-3/4 inches, so check the range printed on the drain before you buy.

Are all kitchen sink drains the same size?

Nearly. Most US kitchen sinks have a 3-1/2 inch hole and use a 1-1/2 inch tailpiece. Some strainers are made to cover 3-1/2 to 4 inch openings. Sink thickness can still rule a strainer out, so check that too.

Can I connect a 1-1/4 inch drain to a 1-1/2 inch trap?

Yes. Reducing slip washers and 1-1/2 by 1-1/4 inch adapters are made for exactly that. You cannot go the other way and shrink a kitchen drain onto 1-1/4 inch pipe without slowing it.

What is the drain hole size for a vessel sink?

Vessel sinks usually take a standard bathroom-size drain, but the drain body must be long enough to pass through the bowl and the countertop together. Check both the hole size range and the maximum thickness.

Sources

Last reviewed October 12, 2026. Parts, sizes and listings change; check the product details before you buy, and follow the maker’s instructions.

Sink drain sizes, drawn to scale