Sold by the foot. 3/16" is the best size for most beer lines under 9' in length. Ideally, 5' provides the correct restriction for serving beer in the 8-14 psi range.
Additional Info: 3/16" line provides 2.2 lbs of restriction per foot. Ideally pounds of resistance should equal pounds of applied pressure. 3/16" line holds 1/6 of an ounce per foot. Made from PVC. 7/16" OD
Tip: If you heat the tubing in a glass of hot water before connecting it will make the whole connection easier on you. Creates a tight connection with 1/4" barb.