What Size is Faucet Supply Line?

A Complete Guide for Kitchen and Bathroom Faucets

[2025-09-04] | By Xiamen Smart Water Technology Co., Ltd. Allen Huang

1. Introduction: Why Faucet Supply Line Size Matters
2. What is a Faucet Supply Line?
3. Common Materials Used in Faucet Supply Lines
4. Standard Faucet Supply Line Sizes

• Diameter Guide
• Length Guide

5. Regional Threading Standards (North America, Europe, Asia)

6. How to Measure Faucet Supply Line Sizes Correctly

7. How to Choose the Right Size for Your Faucet Supply Line

8. Installation Tips for Leak-Free Performance

9. Maintenance and Replacement Best Practices

10. Conclusion & Expert Advice

11. FAQs

The faucet supply line may be small, but it plays a big role in ensuring smooth water flow to your kitchen or bathroom faucet. Whether you're installing a boiling water tap, a traditional kitchen mixer, or a bathroom sink faucet, choosing the correct supply line size is essential for water pressure, leak prevention, and long-term reliability.

A faucet supply line is the flexible or rigid tubing that connects your faucet to the shut-off valve and ultimately to your home's main plumbing system. It ensures consistent water delivery and is designed to withstand varying pressure levels.

Key functions include:

• Delivering water efficiently to the faucet
• Managing water pressure to prevent damage
• Providing installation flexibility in tight spaces
• Preventing leaks when properly sized and installed

Faucet supply lines are available in different materials depending on budget, durability needs, and application:

• Braided Stainless Steel – Highly durable, corrosion-resistant, ideal for long-term use
• Braided Nylon – Lightweight, flexible, cost-effective
• Copper Tubing – Rigid and durable, often used in professional installations

Diameter Guide (Most Common Sizes)

• 3/8 inch – Typical for bathroom sink faucets (up to ~20 GPM flow)
• 1/2 inch – Most common size for both kitchen and bathroom faucets (20–30 GPM flow)
• 5/8 inch – Used in larger or high-flow faucets
• 3/4 inch to 1 inch+ – For main water supply or high-demand applications

👉 Regional standards:

• North America: 9/16-24 compression thread
• Europe: G3/8 thread
• China & Southeast Asia: G1/2 thread

Length Guide (Common Applications)

• 12 inches – Best for compact bathroom sinks with close shut-off valves
• 16 inches – Standard size for most installations
• 20 inches – Common in both kitchens and bathrooms, adds flexibility
• 24 inches – Provides extra reach under kitchen sinks
• 30 inches – Used for unique or extended distance setups

Thread compatibility is critical to avoid leaks. Global markets use different threading systems:

• NPT (National Pipe Thread) – Standard in North America
• BSPT (British Standard Pipe Thread) – Found in Europe and some international markets
• ISO & NPS – Used in select global applications
• Localized Standards – For example, 9/16-24 in the U.S., G3/8 in Europe, and G1/2 in China/SE Asia

• Check the faucet connector (usually under the sink)
• Measure the outer diameter using a caliper or ruler
• Identify threading type (NPT, BSPT, G3/8, G1/2)
• Measure the length from shut-off valve to faucet inlet
• Review manufacturer specifications for brand-specific requirements

• Match the faucet specifications – Always check your faucet manual
• Consider water flow needs – High-flow taps need larger diameters
• Check threading compatibility – Avoid cross-threading by using the correct regional standard
• Choose proper length – Too short = strain & leaks; too long = unnecessary bends
• Select durable materials – Stainless steel braided lines are best for boiling water taps

• Shut off water before installation
• Hand-tighten first, then use a wrench for a snug fit (avoid over-tightening)
• Use Teflon tape on threaded connections if required
• Check for leaks immediately after installation
• Ensure no kinks or sharp bends in flexible lines

• Inspect annually for wear, rust, or cracks
• Replace every 5–10 years, even if no leaks are present
• Flush supply lines to remove sediment buildup
• Use OEM-approved parts when replacing to ensure compatibility with your faucet

Choosing the right faucet supply line size is not just about convenience-it's about ensuring proper water flow, preventing leaks, and extending the lifespan of your kitchen or bathroom faucet. For boiling water taps, selecting the correct size and high-quality material (such as braided stainless steel) is even more critical due to higher temperatures and pressure demands.

If you're sourcing faucet supply lines or complete under-sink drinking water systems, working with a professional manufacturer like Xiamen Smart Water Technology Co., Ltd. ensures reliable quality, global standard compatibility, and ODM/wholesale services for international brands.

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Q1: What is the most common faucet supply line size?
A: In most homes, 1/2 inch and 3/8 inch supply lines are the standard.

Q2: Can I use a longer supply line than required?
A: Yes, but avoid excessive bends, which may reduce water flow.

Q3: How often should faucet supply lines be replaced?
A: Typically every 5–10 years, depending on material quality.

Q4: Do boiling water taps need special supply lines?
A: Yes, it's recommended to use high-quality stainless steel braided lines designed to handle higher temperatures and pressure.