Calculation reviewed: 4 October 2026 · Engineering Desk Tools
How to use the Control valve Cv and Kv (liquid) calculator
Calculate the required flow coefficient Kv and Cv for a non-choked liquid control valve. Start with measurements or documented values for the equipment and reporting period you actually want to assess. The calculator does not fill in a typical installation for you. Its blank fields help keep a demonstration value from being mistaken for your own operating data.
Choose the required options, enter the values in the labelled units and select Calculate. If a field is rejected, check its range and unit before changing it. The result is accompanied by the equation and assumptions so you can decide whether it answers your engineering question.
Inputs and measurement basis
- Liquid flow rate (m³/h). Liquid flow in m³/h. Run the minimum, normal and maximum cases.
- Pressure drop across the valve (bar). Pressure drop across the valve itself at that flow, not across the whole system. The value must be greater than zero.
- Specific gravity (water = 1). Specific gravity relative to water at the flowing temperature; 1 for water. The value must be greater than zero.
Record the measurement source and operating condition. Retain unrounded values for verification.
Method and interpretation
The flow coefficient describes how much liquid a valve passes for a given pressure drop. For turbulent liquid flow below the choking limit, Kv equals flow times the square root of specific gravity divided by pressure drop. Cv is the same quantity in US units, so Cv is about 1.156 times Kv. A real selection also checks cavitation, flashing and the valve opening at minimum and maximum flow.
Kv = Q × √(SG / ΔP), with Q in m³/h and ΔP in bar. Cv = Kv / 0.865 ≈ 1.156 × Kv.
This is the basic equation for turbulent, non-choked liquid flow. It does not include viscosity correction, choked or flashing flow, cavitation, pipe reducers or valve recovery factors; use the manufacturer sizing method or the IEC 60534-2-1 equations for the final selection. Calculate for minimum, normal and maximum flow and choose a valve whose rated Cv keeps normal flow in the useful part of its travel.
Worked example
This example does not populate the form. Enter your own installation data.
Calculated result: 40.8732 Cv (US units). Required flow coefficient at the entered condition. Select a valve with a larger rated value and check cavitation, choked flow and rangeability.
Check the arithmetic independently using the displayed equation. Retain intermediate precision and compare the final value with your equipment documentation.
Quick-reference table
These illustrative rows retain the worked example assumptions except for the varied input. They are not certified ratings or manufacturer data. Use the form for intermediate values.
Common mistakes
Using the full system pressure instead of the drop across the valve; mixing Kv and Cv; ignoring viscosity for oils; sizing only at maximum flow; picking a valve whose calculated Cv is almost its full rating. Before relying on the output, check the decimal format, unit scale and source of each value. Recheck unusual results against the formula.
Frequently asked questions
Are the example values used automatically?
No. Inputs remain blank when the tool opens or when you clear them. The worked example and table are reading material below the calculator. Enter the actual values you want to check each time, and label saved reports so their context is not lost.
What does the result mean?
The result is the flow coefficient the valve must provide at the entered flow and pressure drop. Choose a valve whose rated Cv or Kv is larger, so that normal flow falls in the useful part of its travel.
Can I use a zero or a negative value?
The allowed range follows the meaning of each input. A divisor needs a positive value; other fields may allow zero. Check the form labels and error message rather than forcing an invalid value. A rejected input must be corrected before a result can be shown.
Is this a final design or equipment approval?
No. This is the basic equation for turbulent, non-choked liquid flow. It does not include viscosity correction, choked or flashing flow, cavitation, pipe reducers or valve recovery factors; use the manufacturer sizing method or the IEC 60534-2-1 equations for the final selection. Calculate for minimum, normal and maximum flow and choose a valve whose rated Cv keeps normal flow in the useful part of its travel. Use the calculation as support for a checked decision, and review equipment documentation and applicable requirements before changing an installation or operating setting.
How can I save or share a calculation?
Calculate first, then use Copy result or Print report. Some maintenance tools also provide a CSV summary. Reports contain your own entered data, so review them before sharing. You can share the public page URL without including plant records or confidential measurements.
How do I report an unexpected result?
Use the Contact page and include the tool URL, input values, units, expected output and the reference you used. Explain the measurement basis. Exclude confidential information.
Related tools and records
Use related calculations with consistent units, periods and equipment scope.
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