Most flexible copper refrigerator water lines have an outside diameter of 1/4 inch. Most flexible plastic water lines for refrigerators come with outside diameters of either 1/4 inch or 5/16 inch, reveals Darrins Plumbing Tips.

What size is a ice maker supply line?

1/4-inch The tubing should have a diameter of 1/4-inch and can be copper line, braided steel line or plastic tubing. Many professionals prefer copper line, but plastic tubing is commonly sold as part of ice maker installation kits.