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Orifice Flow Meter Calculator
Design orifice plate flow meters per ISO 5167 standard
Pipe & Flow
Typical range: 0.2 – 0.75
Fluid Properties
Water: 1000, Air (STP): 1.2
Water: 0.001, Air: 0.000018
ISO 5167 Formula
Q = Cd × Y × E × A × √(2ΔP/ρ)
- Cd = Discharge coefficient
- Y = Expansion factor
- E = Velocity approach factor
- A = Orifice area
Orifice Diameter
50.0mm
Differential ΔP
64.6192kPa
Permanent ΔP Loss
36.6383kPa
Loss Ratio
56.7%
Flow Characteristics
Discharge Coefficient Cd
0.6025
Reynolds Number
176839
Expansion Factor Y
1.000
Beta Ratio β
0.500
Velocities & Pressure Loss
Pipe Velocity
1.7684m/s
Orifice Velocity
7.0736m/s
Differential ΔP
64.6192kPa
Permanent Loss
36.6383kPa
Design Recommendations
✓ Re = 176839 — fully turbulent, good accuracy
✓ β = 0.50 — optimal range (0.3–0.7)
✓ Permanent loss = 36.6 kPa — acceptable
▶Beta Ratio Guidelines
β = 0.2–0.4: High ΔP, high accuracy, high loss
β = 0.4–0.6: Balanced ΔP and loss
β = 0.6–0.75: Low ΔP, lower accuracy, low loss
About Orifice Flow Meters
Orifice plates measure flow rate by creating a differential pressure across a constrained bore. The ISO 5167 standard specifies the discharge coefficient correlation (Reader-Harris/Gallagher) used here. Permanent pressure loss ranges from 40–80% of the differential depending on the beta ratio.