Calculate equivalent pipe length for valves and fittings using the K-factor method.
Equivalent length is the imaginary length of straight pipe that would produce the same pressure drop as a fitting. It lets you add up valve and fitting losses on the same basis as straight-pipe friction. This calculator returns the L_eq value from fitting type and pipe size using K-factor and Crane Technical Paper 410 data.
Equivalent length L_eq = K × D / f_T where K is the fitting's loss coefficient and f_T is the friction factor in fully turbulent flow at the relative roughness of the pipe (≈ 0.026 for 1/2-inch commercial steel, falling toward 0.013 for 24-inch). The simpler ratio L/D per Crane TP-410 bypasses f_T and reports L_eq / D directly: 90° standard elbow 30, 45° elbow 16, gate valve open 8, globe valve open 340, swing check valve 100, tee through-flow 20, tee branch 60. Multiply by pipe ID to get L_eq in same units. Total system pressure drop is the sum of (straight + L_eq) × Darcy–Weisbach friction loss per meter.
A piping engineer adds up 4 × 90° elbows, 2 × tees, 1 globe valve on a cooling loop, gets 460 × D equivalent length, multiplies by ID 50 mm = 23 m extra friction — enough to reduce flow by 8% at constant pump head.
A pump installer verifying a Y-strainer's effect on a 25 mm suction line uses L/D = 60 for half-clogged strainer, adds 1.5 m equivalent length, and confirms the suction friction still leaves enough NPSH margin.
An air-system designer estimating drop across 12 elbows and 2 tees on a 100 m, 50 mm steel line adds 50 m equivalent length, computes total 0.4 bar drop at 5 m³/min — within the 0.5 bar end-of-line budget.
K-factor is more rigorous for fittings whose loss is a fixed fraction of velocity head (sharp elbow, mitre, sudden contraction). L/D works well for fittings whose loss tracks pipe friction proportionally (long-radius elbow, tee through-flow).
Yes. K decreases as Reynolds number rises and as fitting size grows — a 1-inch 90° elbow has K ≈ 0.75, a 4-inch K ≈ 0.31. Crane TP-410 tables list the size dependence explicitly.
Swing check valve L/D = 100, lift check valve L/D = 600 (much higher), ball check L/D = 150. Always check the manufacturer datasheet — actual K can vary 2-3× across brands.