Valve Flow Coefficient (Cv) Calculator
Size control valves or determine operating flow conditions. Enter any two of Cv, flow rate (GPM) and pressure drop (psi) plus the liquid specific gravity, and calculate the third using the standard ISA/ANSI Cv formula.
Solve for
GPM
psi
US gal/min of water at 60 °F per √psi pressure drop
- 1
√(SG ÷ ΔP)
√(1 ÷ 25) = 0.2 - 2
Flow coefficient Cv
Q × √(SG ÷ ΔP) = 50 × 0.2 = 10
How does this calculator work?
Cv = Q × √(SG / ΔP) where Q is flow in US GPM, SG is specific gravity (water = 1.0), and ΔP is the pressure differential in psi. Rearrange for flow (Q = Cv × √(ΔP/SG)) or pressure drop (ΔP = SG × (Q/Cv)²). This ISA/ANSI formula applies to fully open valves with incompressible, non-choked liquid flow.
Formula
How this is calculated
The valve flow coefficient Cv is defined by ANSI/ISA-75.01 as the number of US gallons per minute of water at 60 °F (specific gravity 1.0) that flows through a fully open valve with a pressure differential of exactly 1 psi. It is the universal metric for sizing and comparing control valves.
For any incompressible liquid, the relationship between flow rate Q (GPM), Cv, pressure drop ΔP (psi), and specific gravity SG is: Cv = Q × √(SG / ΔP). Rearranging gives Q = Cv × √(ΔP / SG) and ΔP = SG × (Q / Cv)². This calculator covers all three forms so you can find the unknown in valve selection, system verification, or troubleshooting.
The formula assumes fully turbulent, non-choked flow of a Newtonian liquid with no flashing or cavitation. It does not apply to gases or steam (which require separate ANSI coefficients), and it assumes the valve is fully open. For partially open valves, use the manufacturer's inherent characteristic curve to find the effective Cv at the desired opening fraction.
Frequently asked questions
A higher Cv indicates a larger valve or a more open valve — more flow passes through at the same pressure drop. For example, a valve with Cv = 20 passes twice the flow of a Cv = 10 valve at the same ΔP and fluid.
No — the incompressible liquid formula Cv = Q × √(SG / ΔP) does not account for gas compressibility or expansion. Gas and steam Cv calculations use separate ANSI/ISA equations that include pressure-ratio and specific-heat terms.
Specific gravity is measured at the flowing temperature relative to water at 60 °F (15.6 °C). Water = 1.0, light hydrocarbons 0.5–0.8, concentrated acids 1.4–1.8. Check your fluid data sheet for the temperature-corrected value.
Also known as
TG we-Calculate Editorial Team. (2026). Valve Flow Coefficient (Cv) Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/valve-flow-coefficient-calculator
TG we-Calculate Editorial Team. "Valve Flow Coefficient (Cv) Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/valve-flow-coefficient-calculator.
TG we-Calculate Editorial Team, "Valve Flow Coefficient (Cv) Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/valve-flow-coefficient-calculator
@misc{wecalculate_valve_flow_coefficient_calculator, title = {Valve Flow Coefficient (Cv) Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/valve-flow-coefficient-calculator}}, year = {2026}, note = {TG we-Calculate} }
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