Most methods for estimating head loss treat fittings and valves as “equivalent lengths” of tubing having the same size as the fitting or valve. Table 1 gives equivalent lengths of some common fittings and valves.
For example, a 3/4-inch, 90-degree copper elbow has an equivalent length of 2 ft. of 3/4-inch copper tube. A 3/4-inch copper tee with flow making a 90-degree turn has an equivalent length of 3 ft. Although both fittings accomplish the same thing - turning the flow by 90 degrees - the tee has the greater equivalent length because of its sharp corner vs. the sweeping turn through the elbow.