Control Valve Cv Sizing Calculator

Find the valve flow coefficient (Cv) needed for a liquid flow and pressure drop, or the flow a valve of a given Cv will pass.

Fluid and pressure drop

Specific gravity (water = 1)

Pressure drop across the valve (psi)

Required Cv for a flow

Flow (gpm)

Flow from a known Cv

Valve Cv

Liquids, non-choked flow only. This basic equation does not cover gases, steam, flashing or cavitating liquids, high-viscosity fluids or piping effects. For those, use the valve manufacturer's sizing software or the ISA/IEC 60534 equations.

How it works

Cv is defined as the number of US gallons per minute of water at 60 °F that a valve passes with a 1 psi pressure drop. Flow rises with the square root of the pressure drop and falls as the fluid gets heavier.

Cv = Q × √(SG / ΔP)
Q = Cv × √(ΔP / SG)
Q in gpm, ΔP in psi Kv (m³/h) ≈ 0.865 × Cv

Worked example

Water (SG = 1) at 50 gpm with 25 psi across the valve needs Cv = 50 × √(1 / 25) = 10. That is Kv = 8.65 in metric terms.

Valves are normally selected with margin so that the required Cv falls within the working range of the valve (often 20-80% of travel), not at its maximum.

Common questions

Cv or Kv?

Cv uses gallons per minute and psi. Kv uses cubic meters per hour and bar. Convert with Kv = 0.865 × Cv, or Cv = 1.156 × Kv.

Does valve size equal Cv?

No. Cv depends on the valve's design and trim as well as its line size, so always read it from the valve's data sheet.

Calculations are provided for convenience and education. Verify results against manufacturer sizing data before specifying or purchasing a valve.