What is a minor loss coefficient (K)?

K is a dimensionless coefficient that converts a fitting, valve, bend, entrance or exit into an equivalent head loss using the velocity head: h = K·V²/(2g), where V is the mean pipe velocity. 'Minor' refers to localized losses, distinct from the distributed friction loss along the pipe wall.

What is the K value for a 90-degree elbow?

A standard threaded 90° elbow is about K = 0.9; a flanged regular 90° elbow about 0.3; a long-radius 90° elbow about 0.6 threaded or 0.2 flanged. Values vary with size and manufacturer; use Crane TP-410 or vendor data for final design.

What is the K value of a gate valve versus a globe valve?

Fully open, a gate valve is about K = 0.15–0.2, a ball valve about 0.05, a swing check valve about 2.0–2.5, and a globe valve about 10. The globe valve's tortuous path makes it roughly 50× the loss of a gate valve.

What is the entrance and exit loss coefficient?

A sharp-edged (flush) pipe entrance is K = 0.5; a re-entrant/projecting entrance is about 0.8; a well-rounded entrance is 0.04–0.05. The exit loss from a pipe discharging into a large reservoir is always K = 1.0 (the full velocity head is lost).

All tools

Open Darcy-Weisbach calculator →

Minor Loss Coefficients (K) — Reference

Q: How do I combine minor losses with friction loss?

Sum all fitting K values and add the pipe friction term: h_total = (ΣK + f·L/D)·V²/(2g). For long pipelines minor losses are often negligible; for short runs with many fittings they can dominate. An alternative is the equivalent-length method, adding L_eq = K·D/f to the pipe length.

By Michael Flynn, PE · water resources & dam safety engineer · Last updated Sep 8, 2026

Localized losses from fittings, valves, bends, entrances and exits, by the velocity-head method: h_L = K·V²/(2g), with V the mean pipe velocity. Values are typical for fully-turbulent flow; K varies with size, Reynolds number, and manufacturer — use Crane TP-410 or vendor data for final design.

Entrances & Exits

Component	K
Re-entrant / projecting pipe entrance	0.8–1.0
Sharp-edged (flush) entrance	0.5
Slightly rounded entrance (r/D ≈ 0.1)	0.2–0.25
Well-rounded entrance (r/D ≥ 0.15)	0.04–0.05
Exit (pipe → reservoir), any shape	1.0

Summing K across a real network rather than one fitting? HydroComplete carries these losses through the full conveyance run and ties it back to the watershed.

Bends & Elbows

Component	Threaded	Flanged
90° elbow, regular (standard)	0.9	0.3
90° elbow, long radius	0.6	0.2
45° elbow, regular	0.4	0.2
180° return bend	1.5	0.2
90° bend, smooth (r/D = 4–6)	0.15–0.30
Mitered bend, 90° (no vanes)	1.1–1.3

One new reference card a month, free.

Tees

Component	Threaded	Flanged
Tee, line (run-through) flow	0.9	0.2
Tee, branch flow	2.0	1.0

Valves (Fully Open)

Valve type	K
Ball valve, full bore	0.05
Gate valve	0.15–0.2
Butterfly valve	0.3–1.2
Swing check valve	2.0–2.5
Angle valve	2–5
Globe valve	6–10
Foot valve with strainer (hinged)	0.8–1.5

Gate valves throttle steeply: ¾ open ≈ K 1.0–1.2, ½ open ≈ 5.6, ¼ open ≈ 17+. Always design for the fully-open value unless throttling is intended.

Sudden Expansion & Contraction

Component	K (based on smaller-pipe velocity)
Sudden expansion	K = (1 − A₁/A₂)² = (1 − (d₁/d₂)²)²
Sudden contraction	K ≈ 0.5(1 − A₂/A₁) (0 for no change, 0.5 for exit into pipe)

Combine with friction loss. Total head loss over a run is h = (ΣK + f·L/D)·V²/(2g). For long pipelines, minor losses are often negligible; for short runs with many fittings they can dominate. Equivalent-length alternative: L_eq = K·D/f added to the pipe length.

Sources: Crane Co. Flow of Fluids Through Valves, Fittings, and Pipe (Technical Paper 410). Munson et al., Fundamentals of Fluid Mechanics, Table 8.2. Values are representative; manufacturer/size variation is significant for valves.

Computing pipe head loss? Open the Darcy-Weisbach calculator → · Water main? Use Hazen-Williams. · Whole network? Model it in HydroComplete.

Related cheat sheets and tools

Pair these K values with pipe friction from the absolute roughness (ε) card and the Darcy-Weisbach tool, or with the Hazen-Williams equation and its C coefficients for water distribution. For full pressurized-network or storm-system modeling with junction and structure losses, see Culvert inlet vs outlet control (48-inch CMP).

Minor Loss Coefficients (K) — Reference

Entrances & Exits

Bends & Elbows

Tees

Valves (Fully Open)

Sudden Expansion & Contraction

Related cheat sheets and tools

Get future cheat sheets in your inbox