I'm going to be replacing several shut off valves throughout my home. They are a very old type where the supply line is part of the shut off valve, not it's own separate entity.

I've done this once before for a toilet with great success. Thankfully, the supply line included with the new toilet told me what the outlet size should be on the new shut off valve.

The shut off valves I'm going to be replacing are under bathroom sinks. What is the traditional shut off valve outlet size for that? 1/2" 3/8" 1/4"? Does it really matter?

  • Sticking to "standard" sizes makes future repairs easier and less expensive, so I would say that it does matter. It's so annoying to buy a replacement line for a faucet only to find out that someone put on some odd-ball valve.
    – JPhi1618
    Commented Apr 7, 2016 at 16:02
  • 1/4" seems pretty small for a faucet; you might find it running slower than you'd like. Commented Apr 7, 2016 at 16:08
  • 1
    3/8 is most typical for faucet supply lines around here. I think of 1/4 as being supply for a fridge icemaker and 1/2 as being weirdy old faucets that should probably go away anyway. Commented Apr 7, 2016 at 23:09
  • 2
    Whatever size it is, buy quarter turn valves please ;)
    – Mazura
    Commented Apr 8, 2016 at 6:19
  • 1
    I haven't replaced shutoff valves. But when I stopped at Home Depot to get toilet supply lines and didn't know which size, they said get both (1/2 and 3/8) and return the unused lines. I did that and returned with no questions asked. Commented May 2, 2018 at 16:17

3 Answers 3


About 95% of all faucet and toilet stops are 3/8 compression on the outlet. Of course the input depends on your piping in the house, but usually use half inch IPS


To make thing easier and save trips to Home Depot just replace everything with 1/2" inlet by 3/8" outlet compression. The fact is, no matter what flexible hose you buy 7/8, 1/2, 3/8 inch for the water supply on sink, and toilets the internal diameter is the same about 1/4". Stick with with 1/4" compression on Refrigerators. (Typical)


Use 1/2" IPS outlet angle stops for kitchen and bath faucets. 1/4" compression for refrigerator ice maker.

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