Calculator
Valve Cv Calculator: Flow Coefficient Calculator
Calculate the required flow coefficient (Cv) for a control valve based on flow rate, pressure drop, and fluid properties. Select the right valve size for your application.
Interactive toolUpdated July 2026
Inputs
For water at 1 GPM, 1 psi drop: Cv = 1
Water = 1.0
Across the valve at design flow
Results
Required Cv
22.36
At design flow conditions
Recommended Valve Cv
33.54
1.5× safety margin for normal operation at 40–70% travel
Operating Travel (estimated)
~67%
Target: 30–70% of rated travel
The Cv Formula
For liquids, the flow coefficient is:
Cv = Q × √(SG / ΔP)
Where: Q = flow rate (US GPM), SG = specific gravity, ΔP = pressure drop (psi)
Example: 50 GPM of water (SG = 1.0) with a 5 psi pressure drop:
Cv = 50 × √(1.0 / 5) = 50 × 0.447 = 22.4
Select a valve with a rated Cv of approximately 33–35 (1.5× the required Cv), so that normal operation is at 40–70% of valve travel.
Valve Selection Tips
- The rated Cv should be 1.5–3× the required Cv for good controllability
- If the valve operates at less than 20% travel, it's oversized — poor control resolution
- If the valve operates at more than 80% travel, it's undersized — no capacity margin
- For gases, the Cv formula is different — see our Valve Sizing guide for the gas formula
- Always verify the valve can pass maximum flow at full travel (rated Cv ≥ required Cv at max flow)
- Check valve authority: ΔP_valve / (ΔP_valve + ΔP_system) should be ≥ 0.25