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Valve Cv and Kv Calculator

Cv tells you how much water a valve passes at a 1 psi drop. Use it to find the pressure drop at your flow, the flow at a given drop, or the Cv you need.

Method reviewed October 26, 2026. Version 1.0.0. How it works

Your inputs

Unit system

From the valve manufacturer (usually the value at full open). If you have Kv, Cv = Kv ÷ 0.865.

1.0 for water. Glycol mixtures are typically a little above 1; use the fluid supplier’s value.

Result

Pressure drop
6.782psi

Cv 96: 250 gpm at 6.78 psi (SG 1).

  • Valid for liquids well away from flashing or cavitation. Gas and steam valves need different equations.
Cv
96
Kv (m³/h at 1 bar)
83.04
Flow
250gpm
Pressure drop as head of the liquid
15.66ft
Show the working
  1. Liquid valve equation: Q = Cv × √(ΔP ÷ SG)
    ΔP = 1 × (250 ÷ 96)² = 6.782 psi
  2. Kv = Cv × 0.865 (from the unit definitions)
    96 × 0.86498 = 83.038

What Cv means

A valve’s flow coefficient Cv is the number of US gallons per minute of 60 °F water that pass through it with a 1 psi pressure drop. Flow rises with the square root of the pressure drop: Q = Cv × √(ΔP ÷ SG), where SG is the liquid’s specific gravity (1.0 for water).

The University of Florida’s extension guide to irrigation valves gives a worked example: a valve with a Cv of 96 passing 250 gpm drops about 6.7 psi.

Kv and other cautions

Kv is the metric equivalent: cubic metres per hour of water at a 1 bar drop. From the unit definitions, Kv = 0.865 × Cv.

  • Cv is usually published for the fully open valve; it falls as the valve closes.
  • The simple equation is for liquids away from flashing and cavitation. Gas and steam need different equations.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

Calculate
Pressure drop from Cv and flow
Flow
250 gpm
Valve Cv
96
Specific gravity of the liquid
1

Result

Cv
96
Kv (m³/h at 1 bar)
83.04
Flow
250 gpm
Pressure drop
6.782 psi
Pressure drop as head of the liquid
15.66 ft

Cv 96: 250 gpm at 6.78 psi (SG 1).

Assumptions

  • Cv is the US gpm of 60 °F water that passes with a 1 psi drop; flow scales with √(ΔP ÷ SG).
  • Kv = 0.865 × Cv (equivalently Cv = 1.156 × Kv).

Limitations

  • Not for gases, steam, flashing or cavitating liquids, or very viscous fluids.
  • A valve’s Cv falls as it closes; use the manufacturer’s Cv at the opening you expect.

Frequently asked questions

What is the pressure drop through a Cv 10 valve at 20 gpm?

For water, (20 ÷ 10)² = 4 psi.

How do I convert Kv to Cv?

Cv = Kv ÷ 0.865, or about 1.156 × Kv.

Does glycol change the answer?

Yes, through its specific gravity: a higher SG gives a larger drop at the same flow. Use the fluid supplier’s value.

Sources

  1. Valves in Irrigation Systems (CIR824/WI005) — D. Z. Haman, F. S. Zazueta et al., UF/IFAS Extension, University of Florida. Cv is the gallons per minute of 60 °F water that flow through the valve at a 1 lb/in² pressure drop; for water Q = Cv √ΔP; Example 2: Cv 96 at 250 gpm gives (250 ÷ 96)² = 6.7 psi.
  2. NIST Guide to the SI (SP 811), Appendix B.8 — factors for units listed alphabetically — National Institute of Standards and Technology. To pascals: inch of water, conventional 249.0889; inch of mercury, conventional 3,386.389; millimeter of mercury, conventional 133.3224; torr 133.3224; psi 6,894.757; bar 1 × 10⁵; millibar 100; standard atmosphere 101,325.

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