Calculate the valve flow coefficient (Cv) for liquid or gas flow. Enter your inlet pressure (P1), outlet pressure (P2), flow rate, specific gravity, and fluid temperature to get the required Cv value — or flip the calculation to find flow rate from a known Cv. Supports multiple pressure and flow rate units.
Required Cv
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Pressure Drop (ΔP)
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Flow Rate (Q)
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Recommended Cv (×1.3 safety factor)
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The Cv flow coefficient measures a valve's capacity to pass fluid. By definition, a Cv of 1 means 1 US gallon of water at 60°F will flow through the valve per minute with a 1 psi pressure drop. A higher Cv indicates a larger flow capacity.
For liquids, Cv = Q × √(SG / ΔP), where Q is the flow rate in GPM, SG is the fluid's specific gravity relative to water at 60°F, and ΔP is the pressure differential across the valve in psi. This formula is standardized by ISA and widely used in valve sizing.
Specific gravity (SG) accounts for the fluid's density relative to water. Water at 60°F has SG = 1.0. Heavier fluids (SG > 1) require a larger Cv for the same flow rate, while lighter fluids (SG < 1) require a smaller Cv. Always use the SG at operating temperature for accurate results.
This calculator accepts inlet and outlet pressure in PSIA, PSIG, kPa, bar, and MPa. It automatically converts your selected units to psi internally to compute ΔP and Cv. Note: gas calculations typically use absolute pressure (PSIA), not gauge pressure (PSIG).
No. Always select a valve with a Cv somewhat larger than the calculated value to ensure adequate flow and account for real-world variations. A common rule of thumb is to add a safety factor of 1.3× — meaning choose a valve with Cv at least 30% above the calculated minimum.
Cv is the flow coefficient used in the US, defined using US gallons per minute and psi. Kv is the metric equivalent, defined using cubic meters per hour and bar. The conversion is: Kv = Cv × 0.865, or Cv = Kv × 1.156.
Yes. When Gas is selected as the medium type, the calculator uses a simplified compressible flow approximation. For highly accurate gas valve sizing, additional factors such as specific heat ratio, compressibility factor (Z), and critical pressure ratio should be considered in more advanced calculations.
If there is no pressure differential (ΔP = 0), the Cv formula involves division by zero, which is mathematically undefined. In practice, there must be a pressure drop across the valve to produce flow. This calculator will flag a zero or negative ΔP as an invalid input.