Flow Coefficient Calculator

Valve sizing using the flow coefficient C_v (US) and K_v (metric) for incompressible liquid service.

Fluid Mechanics II

Common fluids — click to auto-fill density

Inputs

Solve for:

Flow rate Q (m³/h)

Pressure drop ΔP (bar)

Fluid density ρ (kg/m³)

SG = ρ / 999.1 · C_v reference: water at 15°C (SG = 1)

Theory

Liquid service — C_v (US, ISA standard):

C_v = Q[gal/min] / √(ΔP[psi] / SG)

Q[gal/min] = C_v × √(ΔP[psi] / SG)

ΔP[psi] = SG × (Q[gal/min] / C_v)²

Metric equivalent — K_v (IEC standard):

K_v = Q[m³/h] / √(ΔP[bar] / SG)

C_v = 1.1561 × K_v K_v = C_v / 1.1561

Where:

C_v = US flow coefficient [US gal/min per √psi]
K_v = metric flow coefficient [m³/h per √bar]
Q = volumetric flow rate
ΔP = pressure drop across valve
SG = specific gravity relative to water at 15°C (999 kg/m³)

Typical valve C_v values:

Valve	C_v (approx.)
Ball valve ½″ full-open	14
Ball valve 1″ full-open	61
Ball valve 2″ full-open	250
Globe valve 1″	11
Globe valve 2″	45
Butterfly valve 2″	75
Butterfly valve 4″	600

Gas and steam service

This calculator applies to incompressible liquid service only. Gas and steam Cv calculations require additional correction factors for compressibility, critical flow (choked flow), and specific heat ratio. Use the ISA 75.01 / IEC 60534-2-1 standard for those cases.