The standard US bathroom sink supply line is 3/8-inch compression at the shutoff valve and 1/2-inch FIP at the faucet, usually 20 inches of braided stainless steel.
For the full breakdown, see our best Bathroom Sink Supply Lines guide.
Get the valve end wrong and the line leaks or won’t seat; get the faucet end wrong and you’re back at the store. Most US residential bathroom sinks run the same setup: 3/8-inch compression on the valve side, 1/2-inch FIP on the faucet side, 20 inches of braided stainless steel. The valve end is the match point that trips up most people, so that’s where to start measuring.
References & Sources
- Home Depot. “Residential Water Supply Line Sizing” Confirms the 3/8-inch compression and 1/2-inch FIP standard for US bathroom sinks.
- Home Depot. “Bathroom Plumbing Rough-In Dimensions” Supports supply line placement and rough-in height figures.
- City of Akron Water Supply Bureau. “Water Service and Houseline Connections With Recommended Pipe Sizes for Water Fixtures” Municipal reference for water supply connection sizing.