Cv / Kv / Av Flow Coefficient Converter
Convert any valve flow coefficient — Cv (US), Kv (metric), or Av (SI flow area) — into the other two instantly. Most converters stop at Cv↔Kv; this is a true three-way converter built on the exact IEC 60534-1 constants, with the derivation shown so you can trust the numbers.
The exact conversion constants
Where 0.865 comes from
Cv is gpm of water at 1 psi; Kv is m³/h of water at 1 bar. Converting units: 1 US gpm = 0.227125 m³/h and 1 psi = 0.0689476 bar, so Kv/Cv = 0.227125 / √0.0689476 = 0.86497. That is the exact factor, not an approximation — sources that quote 0.857 are using an older rounding.
Definitions
| Coefficient | Definition | Standard |
|---|---|---|
| Cv | US gpm of 60 °F water at ΔP = 1 psi | ISA-75.01 / IEC 60534 |
| Kv | m³/h of 5–40 °C water at ΔP = 1 bar | IEC 60534-1 |
| Av | m³/s of water at ΔP = 1 Pa (coherent SI flow-area coefficient, m²) | IEC 60534-1 |
Historical caution: the old VDI/VDE Kv was defined at 1 kgf/cm² (≈0.981 bar), not 1 bar. Modern Kv uses 1 bar.
Frequently Asked Questions
How do I convert Cv to Kv?
Multiply Cv by 0.865: Kv = 0.865 × Cv. To go the other way, Cv = 1.156 × Kv. The factor comes from the unit difference (gpm at 1 psi vs m³/h at 1 bar).
What is Av and how does it relate to Cv and Kv?
Av is the coherent-SI flow coefficient with units of m², defined as the flow in m³/s of water at a 1 Pa pressure drop. It converts as Av = 2.40 × 10⁻⁵ × Cv = 2.778 × 10⁻⁵ × Kv.
Why do some sources say Kv = 0.857 × Cv?
0.857 is an older rounded value. The exact factor derived from current unit definitions is 0.86497, normally written 0.865. The difference is under 1% but 0.865 is the IEC-consistent value.
What is the difference between Cv and Kv?
They measure the same thing — valve flow capacity — in different unit systems. Cv uses US gallons per minute at 1 psi; Kv uses cubic metres per hour at 1 bar. Cv is common in North America, Kv in Europe and Asia.
Which coefficient should I use?
Use whichever matches your project standard and region: Cv for US/imperial documentation, Kv for metric/IEC documentation. They are interchangeable through the conversion factors above.
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