Valve Kv and Cv Calculator (Flow Coefficient, Valve Sizing)
The Kv or Cv a valve needs for a given liquid flow and pressure drop, the flow a valve of known Kv passes, and the drop it gives at your flow — with the flow-against-pressure curve.
Results
The dashed line marks the value you entered.
What this tool does
Kv is the flow of water in m³/h that gives a pressure drop of 1 bar across the valve; Cv is the same in US gallons per minute at 1 psi, so Cv = 1.156 × Kv. Flow rises with the square root of the pressure drop (it takes four times the drop to double the flow), which is why a valve sized for the wrong drop is so noticeable. These equations are for liquids in turbulent flow with no flashing or cavitation; for gases, steam, high viscosity or a large drop, use the maker's sizing method.
Formula
Kv = Q √(SG ÷ Δp) (Q in m³/h, Δp in bar) · Q = Kv √(Δp ÷ SG) · Cv = 1.156 × Kv (Cv in US gpm and psi)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
q | Liquid flow through the valve | m³/h |
dp | Pressure drop across the valve | bar |
sg | Specific gravity of the liquid (water = 1) | — |
kv | Kv of the valve you are considering | — |
KR | Kv required | — |
CR | Cv required | — |
QV | Flow that valve passes at that pressure drop | m³/h |
DV | Pressure drop that valve gives at that flow | bar |
UT | Share of the valve's Kv that you need | % |
Worked example
- Liquid flow through the valve10 m³/h
- Pressure drop across the valve0.5 bar
- Specific gravity of the liquid (water = 1)1
- Kv of the valve you are considering16
- Kv required14.14
- Cv required16.35
- Flow that valve passes at that pressure drop11.31 m³/h
- Pressure drop that valve gives at that flow0.391 bar
- Share of the valve's Kv that you need88 %
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.