Control Valve Kv and Cv Sizing Calculator

The flow coefficient Kv (and Cv) a valve needs to pass a liquid flow at a given pressure drop.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

The flow coefficient Kv is the flow of water in cubic metres per hour that gives a pressure drop of 1 bar across the valve. For any liquid, the Kv needed is the flow times the square root of the specific gravity divided by the pressure drop. Cv is the US equivalent, about 1.156 times Kv.

Pick a valve whose full-open Kv is larger than the one you need, so that the valve works within about 20 to 80 percent of its opening. This is for a liquid without flashing or cavitation: gases, steam and flashing liquids need different equations.

Formulas used

  • K_v = Q\sqrt{\frac{SG}{\Delta p}}
  • C_v = 1.156\,K_v

Worked example

With the default numbers in the calculator above:

  1. Flow coefficient Kv: 20 m³/h
  2. Flow coefficient Cv (US): 23.12

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is the difference between Kv and Cv?

Kv uses cubic metres per hour and bar. Cv uses US gallons per minute and psi. Cv is about 1.156 times Kv.

What pressure drop should the valve take?

A control valve usually takes a significant part of the system pressure drop, often 20 to 50 percent, so that it controls well.

Does it work for steam or gas?

No. Compressible flow needs other sizing equations.

Related calculators

Further reading: White, Fluid Mechanics; Munson, Young and Okiishi, Fundamentals of Fluid Mechanics; Crane Technical Paper 410. IEC 60534 control valve sizing (the standard itself is licensed).

Need a calculator we do not have?

Tell us what you would like to calculate. We read every request and build the most asked-for ones.

We store your request (and your email if you give it) to decide what to build. We do not store the numbers you type into calculators.

Embed this calculator on your own page

Copy this code into your page. The calculator runs inside the frame and links back to Drafting Central.

Need this drawn, designed or checked?

Drafting Central is a mechanical engineering and drafting business in Burleigh Waters on the Gold Coast. A calculator gives you the numbers; we can turn them into drawings and designs.

Need help with a real project?

Talk to Drafting Central →

← All engineering calculators