**Flow coefficient** (Cv) is an imperial measurement and is defined as *the flow of water through a valve at 60°F in US gallons/minute (gpm) at a pressure drop of 1lb/in²*.

**Cv = Q * √ (SG/ ΔP) (units in US GPM, psi)**

Q = Flow in US GPM,

SG = Specific Gravity,

**ΔP** = Differential Pressure (psi)

**Flow factor** (Kv) is the metric equivalent of flow coefficient and is defined as *the flow of water in meters cubed per hour (m³/hr) at a pressure drop of bar*.

**Kv = Q * ****√**** (SG/ ****Δ****P) (units in m3/hr, bar)**

Q = Flow in m3/ hr,

SG = Specific Gravity,

**ΔP** = Differential Pressure (bar)

This
should not be confused with * Discharge Coefficient*
(K) which is a non-dimensional factor of a valve used to calculate flow that
discharges to the environment.

**Relationship between between Cv and Kv is **

Cv = 1.156 Kv ** OR**

Kv = 0.864 Cv

Unit conversions from Imperial to Metric (vice versa):

1 US GPM = 0.227125 m3/hr. 1 m3/hr = 4.402868 US GPM

1 psi = 0.06894757 bar 1 bar = 14.503773773 psi

60 deg F = 15.5 deg C

**Conversion of units of Cv to Kv**

Cv = 1US GPM * **√**
(1/1psi)

Cv = 0.227125 m3/hr * **√** (1/0.06894757 bar)

Cv = 0.2271*3.818* m3/ hr * bar

Cv = 0.864 m3/ hr * bar

Cv = 0.864 Kv

**Conversion of units of Kv to Cv**

Kv = 1 m3/hr * **√**
(1/1bar)

Kv = 4.4028812454 US GPM * 0.2625786985 *1/psi

Kv = 4.4028812454 US GPM * **√** (1/14.503773773 psi)

Kv = 1.1561 US GPM / psi

Kv = 1.156 Cv

**What is its importance?**

- Flow coefficient, Cv, and Flow Factor, Kv, are values used to specify the hydraulic capacity of a control valve.
- Quickly compare different brands of valves and their flow capacities
- Help to select a valve that is the right size (and not oversized) for the application.
- Quickly understand how the valve you select will have an effect on the pressure in your system