A kitchen faucet with water coming out requiring a specific supply line size.

What Size Supply Line is Needed for a Kitchen Faucet? A Complete Guide

If you’re installing a new kitchen faucet or replacing an old one, it’s important to use the right size supply lines to connect the faucet to the water supply. The wrong size can restrict water flow, cause leaks, or not provide enough water pressure. As a retired plumber with decades of experience, I’ve seen the problems caused by using the wrong faucet supply line size. In this post, I’ll walk you through how to determine the proper supply line size for your specific kitchen faucet installation.

The size needed depends on various factors like the model of faucet, type of sink, water pressure, and pipe size. We’ll go over all those variables so you can find the perfect fit. Getting the right supply lines allows your faucet to function optimally with adequate water flow and pressure. Read on to learn the ins and outs of measuring and choosing supply lines for a smooth faucet installation.

What Type of Faucet Are You Installing?

The first thing to identify is what type of kitchen faucet you have. Is it a standard model with separate hot and cold handles and spout? Or is it a pull-down, pull-out, or widespread faucet? The more complex faucets like pull-outs have additional components that require supply lines.

Standard widespread faucets have hot and cold water lines running up to the base. Each line connects to the matching handle. Simple centerset faucets work the same way. These basic types of kitchen faucets use standard 3/8 inch supply lines.

Pull-down and pull-out kitchen faucets add in a spray head and hose that sits beneath the main spout. They require not only hot and cold supply lines but an additional smaller diameter line for the sprayer. This line is usually 1/4 inch.

So the first step is taking note of the particular model of kitchen faucet and what specialized parts it has. This gives you an idea of how many supply lines you need and what sizes those lines must be.

Determine the Size of the Water Supply Lines

Now it’s time to look underneath your sink at the current supply lines. Check the point where they screw into the faucet inlets. There should be some markings indicating the line size.

In most cases, you’ll see either 1/2 inch, 3/8 inch, or 1/4 inch for the line diameters. 1/2 inch and 3/8 inch are the most common for standard sink faucets. The 1/4 inch size is used for the sprayer line if present.

If the lines are older, they may not have size labels. You can use a measuring tape to estimate the diameter or bring one line to the hardware store for comparison. Finding the right replacement is crucial for proper water flow.

Make note of the exact size of each existing line that connects to the faucet. This gives you a starting point for selecting new supply lines. Getting the same sizes ensures the lines will integrate smoothly with the faucet fittings.

How’s the Water Pressure at the Sink?

Before deciding on supply line sizes, it’s a good idea to test the water pressure. Simply turn on the faucet and see how strong the stream is. If flow seems weak, low pressure may be restricting it.

With lower water pressure, going up a size on supply lines can help compensate. For example, use 1/2 inch lines instead of 3/8 inch. The larger diameter allows more water to flow through.

If you have average or high pressure, sticking with the standard line sizes is fine. But if flow seems slow, sizing up may give the faucet more pressure. Checking this early on prevents low flow issues after installing new lines.

What is the Pipe Size Coming from the Water Supply?

Now examine the point where the existing supply lines connect to the main water lines under the sink. These are the branch lines that feed up to the faucet.

Note the size of these pipes. In most cases they will be either 1/2 inch or 3/8 inch copper tubing. Matching the supply line size to the pipe size is optimal.

For example, if the branch pipe is 1/2 inch, using 1/2 inch supply lines keeps the flow consistent. If the pipe is smaller 3/8 inch, you would use 3/8 inch supply lines to connect properly.

Trying to use larger supply lines on smaller pipe often causes problems. But if pressure is low, you may get away with going up a size on the supply lines. Checking your incoming pipe size lets you choose a diameter that integrates with the plumbing system.

Account for Any Connectors, Valves, or Filters

Some faucet installations have additional fittings between the supply lines and water supply pipes. Common additions are quick connect fittings, supply line valves, and filters.

Check for any of these extras and account for the connector sizes when buying supply lines. For example, if using a 1/2 inch valve, get supply lines with the matching 1/2 inch female connector. This ensures everything seals and fits together properly.

Even if the incoming pipe is smaller, choose supply lines that match the largest connector size wherever they attach. A 3/8 inch pipe could run through a 1/2 inch connector or valve before the supply lines. So getting 1/2 inch supply lines allows everything to fit correctly.

Putting it All Together – Finding the Right Size

Now that you know your specific faucet model, inlet sizes, water pressure, supply pipe diameter, and any connectors used, you can determine the proper supply line sizes needed.

Start with the industry standard size for that type of faucet, usually 3/8 inch or 1/2 inch. For pull-downs, add a 1/4 inch line for the sprayer.

Then adjust up or down based on your pressure and pipe size. If low pressure, go up a size if possible. Match any larger connectors along the way.

End with supply lines that have the ideal diameters to integrate with your existing plumbing and provide proper water flow to the faucet.

Using these steps helps narrow down the right choice of supply line size for a smooth faucet installation. With the proper fit, you’ll get years of optimal water flow while avoiding leaks and pressure issues.

Key Points to Remember

  • Check existing supply line sizes and measure diameters if needed
  • Test water pressure at the faucet
  • Note incoming pipe sizes under the sink
  • Account for any connectors or valves in the supply path
  • Start with standard line sizes for that faucet type
  • Adjust up for low pressure or down for connectors smaller than the pipe
  • Choose supply lines that integrate properly at both ends

Finding the right supply line size may take some scrutiny, but avoids problems down the road. With the proper diameter lines hooked up, you can enjoy consistent water flow and pressure from your new kitchen faucet. Just be sure to double check your work! Leaks can still happen with improper installation. But with the right parts fitted correctly, you can admire your handiwork every time you turn on the faucet.