Quick answer: To install kitchen faucet supply lines, connect the 1/2-in ends to the faucet shanks and the 3/8-in ends to the wall shut-off valves, hand-tighten, then finish with a quarter-turn wrench. Measure the distance from valves to faucet base and add a few inches for a gentle curve, attach the hot (red) line to the left valve, and flush both lines for a minute to clear debris.
When you decide to upgrade your sink, learning how to install kitchen faucet hardware properly requires paying close attention to the plumbing beneath the counter. While the beautifully finished spout and handles get all the attention above the deck, the most critical components for preventing water damage are hidden inside your cabinet.
The kitchen faucet supply lines are the flexible hoses that connect your home's hot and cold water shut-off valves to the faucet itself. If your old hoses are stiff, corroded, or leaking, you need to know how to replace kitchen faucet supply lines before a major blowout occurs. Here is everything you need to know about sizing and installing these vital connections.
1. Choosing the Right Supply Lines
Modern braided stainless steel supply lines are the industry standard because they are flexible, highly durable, and resist bursting. Before you buy replacements, you need to determine two factors: length and connection size.
Length: Measure the distance from your wall valves to the bottom of the faucet shanks, and add a few inches for a gentle curve. Hoses that are too short will stretch and strain the fittings, while hoses that are too long can kink or get tangled with your pull-out sprayer hose.
Connection Size: Most standard wall shut-off valves require a 3/8-inch compression fitting, while the connection at the base of the faucet is typically a 1/2-inch FIP (Female Iron Pipe) fitting. Always check your specific faucet’s requirements, as some high-end fixtures now come with proprietary supply lines permanently built into the brass body.
| Feature | Size | Note |
|---|---|---|
| Length measurement | distance from wall valves to faucet base plus a few inches | prevents stretching or kinking |
| Valve connection | 3/8-in compression fitting | standard for shut-off valves |
| Faucet connection | 1/2-in FIP fitting | fits most faucet shanks |
| Installation tip | hand-tighten then quarter-turn wrench | no Teflon tape needed |
2. Preparation and Top-Side Assembly
Before you crawl under the sink to handle the plumbing, assemble as much of the fixture above the countertop as possible. For example, check the manufacturer's manual to see how to install kitchen faucet handle levers or base plates if they came detached in the box. Securing the main body of the faucet tightly to the sink deck first provides a stable base for attaching the hoses underneath.
3. How to Connect the Hoses
Once the main fixture is secured, here is exactly how to install kitchen faucet supply lines safely and securely:
Shut Off the Water: Ensure the hot and cold wall valves are completely turned off.
Attach to the Faucet: Thread the 1/2-inch ends of the supply lines onto the threaded brass shanks dropping down from the faucet. Hand-tighten them, then use an adjustable wrench to give them one additional quarter-turn. Do not use plumber's tape (Teflon tape) on these threads; the hoses have built-in rubber gaskets that create the watertight seal.
Attach to the Wall Valves: Connect the 3/8-inch ends to the shut-off valves on the wall. Again, hand-tighten first, then finish with a wrench. Ensure the hot line (usually marked with red) connects to the hot water valve (typically on the left).
4. Flush and Finish
After the lines are connected, turn the wall valves back on and check the connections with a dry paper towel to spot any microscopic leaks.
Before using the sink for dishes, remove the aerator from the spout and run both hot and cold water for a full minute to flush out any scale or debris dislodged during installation. Once the water runs clear, learn how to install kitchen faucet aerator screens by simply twisting the small mesh cap back onto the tip of the spout (using the provided plastic key if necessary).
Ready to upgrade? Browse our Kitchen Faucets collection at Aqualux Studio.
Related: How to Install a Kitchen Faucet in a Tight Space.
The connection sizes are the same ones used on bathroom faucets; if you only need the size and connector reference, see our faucet supply line size and connector guide.
Written by John Plumber, an experienced plumber who shares his personal opinion and hands-on experience.
This article reflects personal experience, not step-by-step instructions. Always follow the manufacturer's installation guide for your exact model, and hire a licensed plumber if you are not sure. Questions or corrections: support@aqualux.studio.
