What Size Supply Line Is Needed For a Kitchen Faucet

Well, there’s a simple answer to that question, but as with all things simple, there are qualifiers.  So, before we get to an answer, let’s consider some general information about water supply lines, their materials, faucet connector sizes, shut-off valves, and such. 

Quick Answer:

The standard size for a kitchen faucet supply line is 3/8 inches in diameter. This size is common for most residential kitchen faucets and provides an adequate water flow for typical usage. However, some homes may have 1/2-inch diameter supply lines, in which case an adapter may be required to connect the faucet. Always confirm the specifications of your faucet and home plumbing before purchasing

Basic Supply Line Piping Under the Sink

There will be two main lines coming up into that space beneath the kitchen sink:  the hot and cold feeds.  These will be soft copper, will include shut-off valves, and then extend a little bit further to a bit.  The one on the left will be the hot feed, and the one on the right will be the cold water feed.

That bit will be the connector piece into which the supply line will fit and then run up to the faucet.  It will include a compression nut and a rubber washer to seal the joint when the supply line is connected.

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Does Size Really Matter with Standard Faucet Supply Lines?

In this instance, I suppose size does matter, in the sense that it doesn’t need to be more than ½ inch.  That actually is the standard sink supply line size and provides sufficient flow at the standard pressure.  That is the answer to the first question asked above.

The other primary consideration is the fitting size. Faucet connection lines can have one of two female connection fittings: 

  • A ½ inch slip joint, with an insert that slips into the mail connector that with a rubber washer makes the connection tight;
  • A ½ inch outside diameter, similar to a slip joint except without the insert.

Supply Line Materials For The Kitchen Faucet

Some kitchen faucet models come with the water supply lines attached.  This takes the guesswork out of the equation and makes the job easier.  We don’t have to guess what material or size we’ll use, and it answers the question of the fitting size mentioned in the previous section.

Supply line materials today are flexible, and that is the smart choice.  It makes installation easy and is a bit forgiving in length if we run over a little.

The options are:

  • Braided stainless steel
  • Vinyl sleeves

The braided stainless steel an excellent choice for lifespan and solidity.

Some flexible lines come with a faucet locking nut and a compression nut attached.  A rubber washer is all that is needed to seal the connection.

Some of the more expensive water supply lines have a sensor attached to the angle stop valve connection.  In the vent of a sudden drop in water pressure, the sensor turns off an emergency shut off valve in the supply line.

These latter faucet feed lines are easy to install and have a long lifespan, but they are also the most expensive.

Replacing Supply Lines for Your Kitchen Faucet

Supply Line and Tools

Should you ever need to replace a supply line, the process is not complicated.  The initial steps are easy:

  • Gather your tools –  two adjustable wrenches.
  • The job is easier, too, if you use a flexible supply line that comes already with a faucet locking nut and a compression nut.  Then, all you need beyond that is the rubber washer to seal the connections.
  • Turn the water line(s) off, and open the faucet handles.
  • Put a towel down around the copper feed pipe because water is still in the supply line.

Then, loosen the nuts at either end of the supply line and remove it.  Connect the new supply line to the copper feed supply pipe at one end and the faucet at the other.  Remember to insert your rubber washers, turn the nuts with your fingers as far as you can, and use the adjustable wrench to tighten the rest of the way.

Use one wrench to hold the copper pipe steady, but easy here as copper can be soft.  You just want to steady it so as not to torque it in tightening the nut.  Use the other wrench to turn the connector nut.  One wrench will be sufficient to connect the supply line to the faucet end.

Turn the faucet handles off, then turn the water back on and make sure the connections are tight.  Pick up the towel and pat yourself on the back for a job well done.

Kitchen Faucet Supply Lines Aren’t a Complicated Thing

As you see, while there are a few considerations beyond the size of the water supply lines, it’s a pretty straightforward thing. 

  • If the faucet came with flexible lines, locking nuts, and compression fittings, all you need to add to the materials list are rubber washers.
  • If it did not, and you need to pick up connection lines, go the flexible route, and choose the braided stainless steel option for its durability and lifespan.

Installation or replacement is easy and takes less than 30 minutes.  You’ll still have lots of time to get to your next DIY project.

1 thought on “What Size Supply Line Is Needed For a Kitchen Faucet”

  1. We had a plumber come to install a new kitchen faucet but the hole in the counter was too small for the faucet parts. Are there companies that make faucets for smaller holes? We want a single handle with Sprayer attached d and soap dispenser with a small detergent bottle.


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