Natural Gas Flow Rate Calculator

Calculator Form

Calculation method

Pipe diameter (mm)

Gas velocity (m/s)

Line pressure (kPa abs)

Temperature (°C)

Compressibility factor Z

Specific gravity

Dynamic viscosity (Pa·s)

Pipe roughness (mm)

Pipe length (m)

Inlet pressure (kPa abs)

Pressure drop (kPa)

Opening diameter (mm)

Upstream pressure (kPa abs)

Differential pressure (kPa)

Discharge coefficient

Expansion factor

Base pressure (kPa abs)

Base temperature (°C)

Reset

Flow Trend Graph

The graph compares flow rate against changing diameter under the active method assumptions.

Example Data Table

Case	Method	Diameter	Pressure basis	Temperature	Actual flow	Standard flow	Mass flow
Velocity case	Velocity and pipe area	80.0 mm	250.0 kPa(abs)	18.0 °C	180.96 m³/h	475.13 Sm³/h	360.93 kg/h
Pressure drop case	Pressure drop along pipe	150.0 mm	500.0 kPa(abs)	22.0 °C	787.68 m³/h	4,065.76 Sm³/h	2,988.86 kg/h
Orifice case	Differential pressure through opening	50.0 mm	420.0 kPa(abs)	20.0 °C	371.23 m³/h	1,644.06 Sm³/h	1,168.31 kg/h

Formula Used

This calculator uses gas density from the real gas equation. Density equals absolute pressure divided by compressibility, gas constant, and absolute temperature.

For the velocity method, actual volumetric flow equals pipe area multiplied by gas velocity. Standard flow adjusts the actual flow to base pressure and base temperature.

For the pressure drop method, Darcy-Weisbach links pressure loss, friction factor, pipe length, diameter, density, and velocity. The code iterates friction factor with Reynolds number using the Swamee-Jain relation.

For the differential pressure method, flow uses discharge coefficient, expansion factor, opening area, and the square root of pressure drop divided by density.

Key expressions are:

Area = πD²/4
ρ = P / (ZRT)
Q = A × v
ṁ = ρ × Q
Re = ρvD / μ
Qstd = Qactual × (Pactual / Pbase) × (Tbase / Tactual) × (Zbase / Zactual)

How to Use This Calculator

Select the method that matches your field data.
Enter pipe or opening diameter in millimeters.
Fill pressure as absolute pressure, not gauge pressure.
Enter temperature, compressibility factor, viscosity, and specific gravity.
Provide length and pressure drop for the pipe method.
Provide discharge and expansion factors for the opening method.
Set base pressure and base temperature for standard flow.
Press calculate and review the result block above.
Use the chart, example table, and export buttons as needed.

Frequently Asked Questions

1. Why does the calculator ask for absolute pressure?

Gas density depends on absolute pressure. If you only have gauge pressure, add local atmospheric pressure before entering the value.

2. What does the compressibility factor do?

Compressibility corrects ideal gas behavior. A lower Z increases calculated density and changes both mass flow and standard flow estimates.

3. Which method should I choose?

Use velocity when field velocity is known. Use pressure drop for pipeline checks. Use differential pressure for openings, nozzles, or simplified meter studies.

4. Is this suitable for custody transfer calculations?

No. Custody transfer usually needs detailed standards, calibrated meters, composition data, and audited correction methods.

5. Why are standard flow and actual flow different?

Actual flow uses operating pressure and temperature. Standard flow converts the same gas quantity to a common reference condition.

6. What viscosity value is reasonable for natural gas?

Many natural gas studies start near 1.0×10⁻⁵ to 1.2×10⁻⁵ Pa·s. Use laboratory or simulation data when accuracy matters.

7. Why does Reynolds number matter here?

Reynolds number indicates the flow regime. It affects friction factor, pressure loss prediction, and the reliability of turbulent correlations.

8. Can I use mixed units?

Enter values in the shown units only. Convert field data first to avoid hidden scaling errors.