1 1/4 vs 1 1/2 P-Trap for Sink – Which is Perfect for You

Last Updated: August 03, 2022 | By JULIAN GILL

When installing a new or replacement sink, you will need to use correctly sized drain hardware. Deciding to go with a 1 1/4 vs 1 1/2 P-trap?

Kitchen sinks and bathroom sinks can have different needs. One trap size may be more appropriate than the other. You’ll need the best information to decide. Let’s take a look at both choices and show you how to make the correct selection!

Difference Between 1 1/4 and 1 1/2 P trap?

P trap for sink

The main difference between these two P-traps comes down to size. 1 ¼ inch traps will use smaller tubing than 1 ½ inch traps. Larger tubing will take up more space under a sink. In tight spaces, you might need to use a 1 1/4 P trap.

You may need to select one size depending on what fixtures or appliances are being connected. Another factor is the size of existing plumbing. If you are plumbing to an existing drain connector, using the same size of P-trap will remove the need for adapters.

While P-traps are available in metal and plastic versions there can be good reasons to go with one over the other. Will the plumbing be exposed? If so, a metal P-trap can be more decorative. Are you expecting heavy use and frequent maintenance? A plastic P-trap will be less prone to corrosion and easier to disassemble for service if it becomes clogged.

Metal P-traps are at risk from corrosion. Avoid using strong chemicals in these and other metal fittings. Plastic P-traps are corrosion resistant but can be cracked by impact or rough handling. Decide for yourself if these risks will affect your choice.

ProductImageMaterialDimensions (in)
Master Plumber 219-162q? encoding=UTF8&ASIN=B000BPDIQC&Format= SL160 &ID=AsinImage&MarketPlace=US&ServiceVersion=20070822&WS=1&tag=mohmd99 20&language=en US
Brass1.87 x 8 x 12
Westbrass D1838QRL-01q? encoding=UTF8&ASIN=B08B86Z6XK&Format= SL160 &ID=AsinImage&MarketPlace=US&ServiceVersion=20070822&WS=1&tag=mohmd99 20&language=en USBrass‎20 x 6 x 3
GORDEE Bathroom Basin Sink Bottle P Trapq? encoding=UTF8&ASIN=B0936N7KK9&Format= SL160 &ID=AsinImage&MarketPlace=US&ServiceVersion=20070822&WS=1&tag=mohmd99 20&language=en USConstructed: Brass
Pipe: Stainless Steel
‎13.82 x 4.69 x 2.13
ProductImageMaterialDimensions (in)
Dearborn P9703WBG 1-1/2" P-Trapq? encoding=UTF8&ASIN=B00DZTK3L4&Format= SL160 &ID=AsinImage&MarketPlace=US&ServiceVersion=20070822&WS=1&tag=mohmd99 20&language=en USPolypropylene‎6 x 3 x 6
LASCO 03-3431 17-Gaugeq? encoding=UTF8&ASIN=B00HYWBLT6&Format= SL160 &ID=AsinImage&MarketPlace=US&ServiceVersion=20070822&WS=1&tag=mohmd99 20&language=en USBrass‎2 x 10.5 x 5
Westbrass D400-1-01 1-1/2q? encoding=UTF8&ASIN=B004034IPG&Format= SL160 &ID=AsinImage&MarketPlace=US&ServiceVersion=20070822&WS=1&tag=mohmd99 20&language=en USBrass
6 x 3 x 12

How do I know what size P-trap to get?

Sometimes P-trap size is decided for you by the fixtures you choose. Often sinks will come with flanges that need 1 ¼ or 1 ½ connection. When choosing a 1 1/4 vs 1 1/2 P-trap, it’s best to pick the choice that fits existing plumbing connections. Forcing one or the other with size adapters can lead to installation problems and possible leaks in the future.

If in doubt, measure pipe openings with a ruler to find out the diameter. P-traps are sized based on tubing diameter. A 1 ¼ inch opening will need a 1 ¼ inch P-trap. A 1 ½ inch opening will need a 1 ½ inch P-trap.

What size should the kitchen and bathroom P-trap be?

Usually a kitchen sink will need a 1 ½ inch P-trap. While bathroom sinks use 1 ¼ P-traps. Kitchen appliances like garbage disposals often have 1 ½ inch fittings. Installing these is much easier when using standard 1 ½ pipe and fittings.

A professional plumber will usually install a 1 ¼ inch P trap for a bathroom sink and a 1 ½ inch P trap for a kitchen sink. For professionals, the choice between a 1 1/4 vs 1 1/2 P trap is often dictated by local plumbing codes. Some regions will require a specific size of P trap in kitchen and bathroom sinks. It is best to follow local regulations. Contact a professional if you are unsure what rules apply in your city or state.

You might also like:

author of resisories.com julian gill pictureJulian Gill

Julian Gill is a mechanical engineer and Certified in Plumbing Design (CPD) and worked as a plumbing engineer for ten years. Besides this, he is interested in home improvement and currently works as a writer. @JulianGillPro

Disclaimer: As an Amazon Associate I earn from qualifying purchases. And That is a very small commission from purchases made via the links at no additional costs to you. Learn more.

Leave a Comment