Gas Pipeline Sizing Calculator

Calculator inputs

Use absolute pressure values. The calculator supports diameter sizing, flow capacity checks, and pressure drop estimation.

Formula used

1) Standard-to-actual flow conversion

Qactual = Qstandard × (Pbase / Pavg) × (Tline / Tbase) × Z

2) Gas density from average line pressure

ρ = (Pavg × MW) / (Z × R × Tline)

3) Reynolds number

Re = (ρ × v × D) / μ

4) Friction factor

f = 64 / Re for laminar flow, and the Swamee-Jain approximation for turbulent flow.

5) Darcy pressure loss

ΔP = f × (L / D) × (ρ × v² / 2)

6) Diameter sizing logic

The solver iterates diameter until both the allowable pressure drop and the maximum design velocity are satisfied.

How to use this calculator

Choose a calculation mode based on your design task.

Enter the standard flow rate and the line operating conditions.

Use absolute pressures, not gauge pressures.

Add straight length and extra equivalent length for fittings.

Enter gas properties: specific gravity, Z, viscosity, and roughness.

For sizing, enter both inlet and target outlet pressure.

For capacity or pressure drop checks, enter the inside diameter.

Review the result cards, detailed table, graph, and export files.

Example data table

Illustrative examples for quick benchmarking. Use project-specific gas data for actual design work.

Case	Flow (Sm³/h)	Length (m)	Inlet bar(a)	Outlet bar(a)	SG	Z	Indicative ID (mm)
Factory branch line	1,200	180	4.5	4.2	0.60	0.98	50
Boiler fuel header	3,800	420	7.0	6.4	0.62	0.97	100
Plant distribution run	9,500	900	10.0	8.9	0.65	0.95	150

FAQs

1) What does this calculator estimate?

It estimates inside diameter, line capacity, velocity, Reynolds number, friction factor, and pressure drop for a steady gas flow case using entered gas properties and line conditions.

2) Why should I enter absolute pressure?

Gas density and actual flowing volume depend on absolute pressure. Using gauge pressure directly will distort density, velocity, and pressure-loss results.

3) Why is standard flow converted to actual line flow?

Pressure loss depends on actual velocity inside the pipe. Standard flow is convenient for metering, but hydraulic losses require flowing volume under line conditions.

4) When are these results less reliable?

Use caution when pressure drop is large, gas properties change strongly, or transmission conditions are severe. In those cases, confirm with a more detailed compressible-flow method.

5) What roughness value should I use?

Use the expected internal roughness for the pipe material and condition. New, smooth pipe generally uses a lower value than aged or scaled pipe.

6) Why is velocity limit included?

Velocity affects noise, erosion risk, regulator performance, and pressure loss. A practical velocity cap helps keep the selected size within a controllable operating range.

7) Can I use this for gases other than natural gas?

Yes, if you provide reasonable specific gravity, viscosity, compressibility, and operating conditions. Review compatibility, code rules, and safety limits separately for each gas service.

8) Is this enough for final construction design?

No. Treat it as an engineering estimator. Final design should also check applicable codes, fittings, valves, elevation effects, equipment losses, and project safety requirements.