Cv Flow Calculator — Valve Flow Coefficient
Size a control valve or check its flow capacity. Enter any two of flow rate, pressure drop, and Cv — with liquid specific gravity — and the calculator returns the third, plus the metric Kv equivalent and a Q vs ΔP curve for the valve.
Solve for
GPM
psi
Cv is the flow rate in GPM that produces a 1 psi pressure drop for water (SG = 1)
- 1
SG ÷ ΔP
1 ÷ 15 = 0.067 - 2
√(SG ÷ ΔP)
√(0.067) = 0.258 - 3
Flow coefficient Cv = Q × √(SG ÷ ΔP)
10 × 0.258 = 2.582
How does this calculator work?
The valve flow coefficient Cv = Q × √(SG ÷ ΔP), where Q is flow in GPM, SG is liquid specific gravity, and ΔP is pressure drop in psi. Enter any two of Cv, Q, and ΔP (plus SG) to solve for the third. The metric equivalent Kv = 0.865 × Cv (m³/h at 1 bar for water).
Formula
How this is calculated
The flow coefficient Cv (or its SI counterpart Kv) is the single number that characterises a valve's capacity: defined as the flow rate in US gallons per minute of water at 60 °F (SG = 1) that produces exactly 1 psi pressure drop across the valve. A larger Cv means the valve passes more flow at the same differential pressure, or the same flow at a lower differential.
For any liquid, the flow rate scales with the square root of the pressure drop (Torricelli-like behaviour), and inversely with the square root of the liquid's specific gravity — heavier liquids flow less easily at the same pressure. Rearranging Q = Cv × √(ΔP/SG) lets you solve for any unknown given the other two: manufacturers publish Cv at a rated stroke position, and engineers work backwards to find the required differential pressure for a target flow rate, or forward to check whether a nominated valve passes the design flow.
Kv (m³/h flow at 1 bar ΔP for water) is the international metric equivalent: Kv = 0.865 × Cv. The conversion is exact and stems from unit analysis of the underlying orifice equation. These formulas apply only to fully turbulent, non-cavitating, incompressible (liquid) flow. For gas or steam, a separate compressible-flow Cv formula applies.
Frequently asked questions
Cv is the valve flow coefficient: the flow rate in US gallons per minute of water at 60 °F that causes exactly a 1 psi pressure drop across the valve at full open. A higher Cv means the valve has less flow restriction. Manufacturers publish Cv values in their datasheets.
Use the liquid's density divided by the density of water at 60 °F (999 kg/m³ ≈ 1). Water = 1.0, light oils ≈ 0.85–0.90, heavy oils ≈ 0.90–0.97, glycol ≈ 1.11. You can find specific gravity in material safety data sheets or fluid property tables.
No. The formula Cv = Q√(SG/ΔP) assumes incompressible (liquid) flow. Gases and steam require a separate compressible-flow Cv equation that accounts for the inlet pressure, specific heat ratio, and expansion factor. Use a dedicated gas valve sizing tool for those fluids.
Also known as
TG we-Calculate Editorial Team. (2026). Cv Flow Calculator — Valve Flow Coefficient [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/cv-flow-calculator
TG we-Calculate Editorial Team. "Cv Flow Calculator — Valve Flow Coefficient." TG we-Calculate. 2026. https://we-calculate.com/calculator/cv-flow-calculator.
TG we-Calculate Editorial Team, "Cv Flow Calculator — Valve Flow Coefficient," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/cv-flow-calculator
@misc{wecalculate_cv_flow_calculator, title = {Cv Flow Calculator — Valve Flow Coefficient}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/cv-flow-calculator}}, year = {2026}, note = {TG we-Calculate} }
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