Orifice Plate Flow Calculator
Flow rate through an orifice plate from the differential pressure, with the beta ratio and velocities.
Results
Flow rate
2.3979
L/s
Flow rate
8.6323
m³/h
Beta ratio
0.5000
Speed
4.8849
m/s
Speed
1.2212
m/s
What this tool does
The discharge coefficient accounts for the vena contracta — the jet keeps narrowing past the hole — and for friction; about 0.61 is typical for a sharp-edged orifice, while a well-made venturi reaches 0.98. Beta ratios between 0.2 and 0.7 are the usable range, and metering to a standard means following its rules on straight lengths, tapping positions and plate finish.
Formula
Q = Cd A √(2 Δp ÷ ρ) ÷ √(1 − β⁴)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
cd | Discharge coefficient | — |
do | Orifice diameter | mm |
dd | Pipe diameter | mm |
dx | Differential pressure | kPa |
ro | Fluid density | kg/m³ |
QL | Flow rate | L/s |
QH | Flow rate | m³/h |
BT | Beta ratio | — |
VO | Speed | m/s |
VP | Speed | m/s |
Worked example
- Discharge coefficient0.61
- Orifice diameter25 mm
- Pipe diameter50 mm
- Differential pressure30 kPa
- Fluid density998 kg/m³
- Flow rate2.3979 L/s
- Flow rate8.6323 m³/h
- Beta ratio0.5000
- Speed4.8849 m/s
- Speed1.2212 m/s
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.