Cv (flow coefficient) is the number of US gallons per minute of water at 60 °F that will flow through a valve at a 1 psi pressure drop. It is the US/imperial standard for valve sizing defined by ISA-75.01.

What is the difference between Cv and Kv?

Kv is the SI equivalent used in IEC 60534. It represents flow in m³/h of water at 1 bar pressure drop. The conversion is Kv = Cv × 0.8646.

Which formula does this tool use for liquids?

Cv = Q × √(SG / ΔP), where Q is flow in US GPM, SG is specific gravity relative to water at 60 °F, and ΔP is differential pressure in psi.

Which formula is used for gases?

For subcritical gas flow: Cv = Q / (963 × P1 × Y) × √(SG × T / ΔP), where Q is SCFH, P1 is inlet pressure (psia), T is absolute temperature (°R), Y is the expansion factor, and SG is specific gravity relative to air.

What is the expansion factor Y?

Y accounts for the change in gas density as pressure drops across the valve. It ranges from 0.667 (choked flow) to 1.0 (no pressure drop). This tool computes Y automatically from the pressure ratio.

When is gas flow choked?

Choked (critical) flow occurs when ΔP/P1 ≥ 0.42 for a typical valve (Fk = 1). Beyond this point, increasing ΔP no longer increases flow. The tool flags this condition and caps Y at 0.667.

Control Valve Cv Calculator

Name: Control Valve Cv Calculator
Availability: InStock
Author: Nham Vu

Calculate the Cv (flow coefficient) required for a control valve in liquid or gas service using ISA/IEC standard equations.

Valve Sizing Inputs

Fluid Type

Flow Rate (US GPM)

Inlet Pressure P1 (psia)

Outlet Pressure P2 (psia)

Specific Gravity (relative to water; 1.0 = water)

Enter your valve conditions and click Calculate Cv.

Summary

Calculate the Cv (flow coefficient) required for a control valve in liquid or gas service using ISA/IEC standard equations.

How it works

Select the fluid type: liquid or gas/vapor.
Enter the flow rate, inlet pressure, and allowable pressure drop.
Provide fluid properties (specific gravity for liquids; temperature and specific gravity for gas).
The calculator applies the ISA-75.01 / IEC 60534 sizing equation.
Read the required Cv (US) and equivalent Kv (SI) values from the results panel.

Use cases

Sizing globe, ball, and butterfly control valves for process piping.
Verifying that an existing valve can pass required flow without excessive pressure drop.
Converting between Cv and Kv for international valve datasheets.
Preliminary valve selection before running full ISA calculations in plant software.
Educational use to understand valve flow coefficient fundamentals.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu