Fitting and Valve Loss Coefficients (K Factors)
Typical loss coefficients (K) and equivalent lengths for 17 common fittings and valves.
Every elbow, tee and valve in a pipe adds a pressure loss on top of the friction of the straight pipe. It is written as a loss coefficient K: the loss equals K times the dynamic pressure, Δp = K × ρ v² ÷ 2, or in head, h = K × v² ÷ 2g. This table lists typical K values for 17 fittings and valves, for screwed and for flanged or welded connections, and the equivalent length of straight pipe in pipe diameters.
The table
| Fitting or valve | Loss coefficient K, screwed | Loss coefficient K, flanged or welded | Equivalent length in diameters, screwed (L/D) | Equivalent length in diameters, flanged (L/D) |
|---|---|---|---|---|
| Standard 90 degree elbow | 0.9 | 0.3 | 45 | 15 |
| Long radius 90 degree elbow | 0.6 | 0.2 | 30 | 10 |
| 45 degree elbow | 0.4 | 0.2 | 20 | 10 |
| 180 degree return bend | 1.5 | 0.2 | 75 | 10 |
| Tee, flow straight through | 0.9 | 0.2 | 45 | 10 |
| Tee, flow into or out of the branch | 2 | 1 | 100 | 50 |
| Gate valve, fully open | 0.2 | 0.2 | 10 | 10 |
| Gate valve, one quarter closed | 0.3 | 0.3 | 15 | 15 |
| Gate valve, half closed | 2.1 | 2.1 | 105 | 105 |
| Gate valve, three quarters closed | 17 | 17 | 850 | 850 |
| Globe valve, fully open | 10 | 10 | 500 | 500 |
| Angle valve, fully open | 5 | 5 | 250 | 250 |
| Ball valve, fully open | 0.05 | 0.05 | 3 | 3 |
| Swing check valve | 2 | 2 | 100 | 100 |
| Pipe entrance, sharp edge | 0.5 | 0.5 | 25 | 25 |
| Pipe entrance, well rounded | 0.03 | 0.03 | 2 | 2 |
| Pipe exit into a tank | 1 | 1 | 50 | 50 |
Source and notes: Typical loss coefficients for turbulent flow (Cengel and Cimbala, Fluid Mechanics, Table 8-4; Crane TP-410). The pressure loss is K x (density x velocity squared / 2); the head loss is K x velocity squared / (2 g). The equivalent length is K divided by a typical friction factor of 0.02 (fully rough flow in medium pipe); makers' data for the exact valve is always better.
How to use this table
- Find each fitting and valve in the pipe run and read its K.
- Add the K values and multiply by ρ v² ÷ 2 for the pressure loss (or v² ÷ 2g for the head loss).
- Add this to the friction loss of the straight pipe.
Worked example: six screwed elbows and a globe valve with water at 2 m/s
- Total K = 6 × 0.9 + 10 = 15.4.
- Pressure loss = K × ρ v² ÷ 2 = 15.4 × 998 × 2² ÷ 2 = 30.7 kPa.
- In head: K v² ÷ 2g = 15.4 × 4 ÷ 19.62 = 3.14 m of water.
Notes and cautions
- K varies with pipe size and Reynolds number; the figures are typical for turbulent flow in medium-size pipe. Large valves and small valves differ.
- A globe valve costs far more pressure than a ball valve or a fully open gate valve: choose by the loss when flow control is not needed.
- Partly closed valves have much higher K, which is how throttling works.
Related tools and guides
- Fittings, Valves and Minor Losses (guide)
- Pipe Flow and Pressure Drop Calculator
- Pipe Roughness Values
- Steel Pipe Sizes (NPS and DN, Schedule 40 and 80)
- All reference tables
FAQ
What is the K factor of a 90 degree elbow?
About 0.9 for a standard screwed elbow and 0.3 for a flanged one, or 0.2 for a long-radius flanged elbow.
What is a loss coefficient?
A number that multiplies the dynamic pressure (ρ v² ÷ 2) to give the pressure lost in a fitting.
What is equivalent length?
The length of straight pipe that would give the same pressure loss: K divided by the pipe friction factor, here taken as 0.02.
Sources
- Cengel and Cimbala, Fluid Mechanics, Table 8-4; Crane Technical Paper 410, Flow of Fluids Through Valves, Fittings and Pipe; Hooper’s two-K method for more accuracy.
- Typical loss coefficients for turbulent flow (Cengel and Cimbala, Fluid Mechanics, Table 8-4; Crane TP-410). The pressure loss is K x (density x velocity squared / 2); the head loss is K x velocity squared / (2 g). The equivalent length is K divided by a typical friction factor of 0.02 (fully rough flow in medium pipe); makers' data for the exact valve is always better.