Pipe Fittings Pressure Drop Calculator (K Factor)
Find the pressure drop through pipe fittings and valves. K values use the Crane equivalent length (L/D) method with the fully turbulent friction factor for the pipe size.
- fT = 0.25 ÷ [log₁₀(ε ÷ 3.7D)]² with ε = 0.045 mm = 0.0162
- K = (L/D) × fT for each fitting; total K = 4.155
- ΔP = K × ρv²/2 = 4.155 × 1,427 Pa = 59.3 mbar
Fittings used
| Fitting | L/D | K each | Qty | K total |
|---|---|---|---|---|
| 90° standard elbow | 30 | 0.487 | 4 | 1.948 |
| Tee, run | 20 | 0.325 | 1 | 0.325 |
| Gate valve | 8 | 0.130 | 2 | 0.260 |
| Swing check valve | 100 | 1.623 | 1 | 1.623 |
Fitting Loss Formulas (Crane Method)
K = (L/D) × fT
fT = 0.25 ÷ [log₁₀(ε ÷ 3.7D)]²
L/D is the equivalent length ratio of each fitting (gate valve 8, ball valve 3, globe valve 340, swing check 100, standard 90° elbow 30, 45° elbow 16, tee run 20, tee branch 60), fT the fully turbulent friction factor of clean commercial steel at the pipe size, ε = 0.045 mm, v the velocity and ρ the density. Entrance (K = 0.5) and exit (K = 1.0) are fixed. Add straight pipe loss separately with the pipe pressure drop calculator.
Worked example
50 m³/h of water in a 4" Sch 40 line (ID 102.26 mm, 1.69 m/s) through 4 elbows, 1 tee run, 2 gate valves and 1 swing check: total K ≈ 4.16 and ΔP ≈ 59 mbar.
Frequently Asked Questions
What is a K factor?
The resistance coefficient of a fitting: the number of velocity heads lost through it. ΔP = K × ρv²/2.
What is the Crane method?
K values are found from a fixed equivalent length ratio L/D for each fitting type times the fully turbulent friction factor of the pipe size, from Crane Technical Paper 410.
Do I also need the straight pipe loss?
Yes. Fitting losses are added to the friction loss of the straight pipe for the total system pressure drop.
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