What Is Kv Value? Metric Flow Coefficient

Quick Answer

Kv is the metric flow coefficient for valves. It is defined as the flow of water in cubic meters per hour (m3/h) at a temperature of 5-30 degC through a fully open valve with a pressure drop of 1 bar. Kv is the European and international equivalent of Cv (used in North America). The conversion is Cv = 1.156 x Kv, or Kv = 0.865 x Cv. Kv is defined in IEC 60534 and EN 60534.

Definition and Formula

Parameter	Symbol	Unit
Flow coefficient (metric)	Kv	m3/h at 1 bar delta-P (water, 5-30 degC)
Flow rate	Q	Cubic meters per hour (m3/h)
Pressure drop	delta-P	bar (P1 - P2)
Specific gravity	G	Relative to water (water = 1.0)

Liquid flow formula:

Kv = Q x sqrt(G / delta-P)

Example: A valve must pass 50 m3/h of water (G=1.0) at 2 bar pressure drop.

Kv = 50 x sqrt(1.0 / 2) = 50 x 0.707 = 35.4

A valve with rated Kv of 35.4 or higher is required.

Kv to Cv Conversion

From	To	Formula
Kv	Cv	Cv = 1.156 x Kv
Cv	Kv	Kv = 0.865 x Cv

The conversion factor (1.156) accounts for the unit differences: US gallons vs cubic meters, psi vs bar. These are exact relationships; no approximation.

Conversion Examples

Kv (m3/h)	Cv (US GPM)
10	11.56
25	28.9
50	57.8
100	115.6
250	289
500	578
1,000	1,156

Kv Values by Valve Type

Valve Type	DN 50	DN 100	DN 150	DN 200	DN 300
Full bore ball valve	117	554	1,272	2,285	4,671
Gate valve	104	510	1,168	2,163	4,412
Globe valve	26	95	182	294	606
Butterfly valve	69	415	1,038	1,903	4,153

Where Kv Is Used

Region/Standard	Flow Coefficient	Reference
North America (API, ISA)	Cv	ISA/IEC 60534 (US customary)
Europe (EN, DIN)	Kv	IEC 60534, EN 60534
International (ISO)	Kv (preferred) or Cv	IEC 60534 supports both
Manufacturer datasheets	Both Kv and Cv typically listed	Dual reporting common

Kv in Control Valve Sizing

IEC 60534 provides comprehensive sizing equations in both Cv and Kv formats. For European projects, valve datasheets, specifications, and control valve sizing calculations use Kv exclusively. When reviewing specifications from different regions, always verify which coefficient is used before sizing:

Sizing Parameter	Cv System	Kv System
Flow units	US GPM	m3/h
Pressure units	psi	bar or kPa
Temperature units	degF	degC
Pressure recovery factor	FL (same)	FL (same)
Piping geometry factor	FP (same)	FP (same)

The sizing methodology is identical; only the units differ. Using Cv values in a Kv equation (or vice versa) without conversion produces a 15.6% error; enough to cause serious over- or undersizing.

Common Mistake

Mixing Cv and Kv values on the same datasheet or calculation without conversion. This is especially common when combining American valve manufacturer data (Cv) with European project specifications (Kv). Always verify the coefficient type and convert before comparing or sizing.

Read the full guide to valve types