Natural Gas Pipeline Diameter Calculator

Calculator Inputs

Flow Rate (MMSCFD)

Pipeline Length (km)

Inlet Pressure (bar g)

Outlet Pressure (bar g)

Gas Specific Gravity

Gas Temperature (°F)

Efficiency Factor

Pipe Roughness (mm)

Design Margin Factor

Velocity Limit (ft/s)

Output Diameter Unit

Example Data Table

Flow (MMSCFD)	Length (km)	Pin (bar)	Pout (bar)	SG	Temp (°F)	Efficiency	Diameter (in)
12	18	42	37	0.62	60	0.92	6.39
25	45	55	47	0.64	70	0.9	8.5
40	70	68	56	0.6	80	0.88	10.28

Formula Used

This calculator uses a rearranged Weymouth-style gas transmission relationship for preliminary diameter sizing. It estimates pipe diameter from flow, line length, specific gravity, temperature, inlet pressure, outlet pressure, and an overall efficiency factor.

Flow form:
Q = 433.5 × E × D^2.667 × √((P₁² − P₂²) / (SG × T × L))

Diameter form:
D = [Q / (433.5 × E × √((P₁² − P₂²) / (SG × T × L)))]^1/2.667

Where Q is gas flow in MMSCFD, D is internal diameter in inches, E is efficiency, P₁ and P₂ are absolute pressures, SG is gas specific gravity, T is temperature in Rankine, and L is pipe length in miles.

The velocity shown is an approximate screening value derived from estimated actual flow under average line pressure. Final engineering design should confirm compressibility, elevation, fittings, roughness, code compliance, and transient behavior.

How to Use This Calculator

Enter the expected gas flow rate in MMSCFD.
Provide the planned pipeline length in kilometers.
Enter inlet and outlet gauge pressures in bar.
Set gas specific gravity and operating temperature.
Choose an efficiency factor reflecting practical line behavior.
Add a design margin factor if you want a conservative result.
Specify a preferred velocity limit for screening.
Click calculate to show results above the form.
Review diameter, nominal size, velocity, and pressure metrics.
Use the chart and exports for quick reporting.

Frequently Asked Questions

1. What does this calculator estimate?

It estimates a preliminary internal pipeline diameter for natural gas service using flow, pressures, length, gas properties, and an efficiency factor.

2. Is this suitable for final design approval?

No. It supports screening and planning. Final design should include code checks, wall thickness, stress analysis, compressibility, fittings, elevation, and regulator effects.

3. Why are inlet and outlet pressures both needed?

The usable pressure differential drives gas movement. A smaller drop usually requires a larger diameter to carry the same flow over the same distance.

4. What is the efficiency factor?

It is a practical correction for real-world behavior. Lower values make the calculated diameter larger, reflecting extra losses or conservative assumptions.

5. Why does the calculator show gas velocity?

Velocity is a useful screening check. Excessive velocity can increase noise, erosion risk, and operating losses, so it helps identify undersized lines.

6. Can I use millimeters instead of inches?

Yes. The result can display in inches or millimeters, while the internal calculation still uses consistent engineering unit conversions.

7. What does the design margin factor do?

It increases the calculated diameter by your selected multiplier. This is useful when you want additional conservatism for future capacity or uncertainty.

8. Which pipeline equation is used here?

A rearranged Weymouth-style relationship is used for preliminary transmission-type sizing. It is common for quick gas line estimates under steady assumptions.