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.TT pocketEngineer softDesign - where pocketEngineer software lives...
 Gas Pipe Sizing Calculator (pocketGas v7.14)

high & low pressure gas pipeline hydraulic calculations - find flowrate, pipe size & pressure drop



To take a glance at all pocketEngineer software and OS requirements, click Overview.


For Android OS, see aPocketGas.


Note: pocketGas (Windows) and aPocketGas (Android) are not the same.


pocketGas (Gas Pipe Sizing Calculator):  

your mobile design partner for Gas pipe design & sizing 

Natural Gas or LPG (Propane) pipe sizing for high pressure & low pressure systems is as easy as 1, 2, 3 with pocketGas (Gas Pipe Sizer) program. pocketGas calculates gas flowrate, pipe size and pressure drop. The oldest and most common equation - Weymouth equation - is used in the high pressure gas calculation. NFPA model for high pressure calculation is also included. For low pressure gas calculation, NFPA equation is used.

Aim: creating a mobile design environment (
ShowMe!) for the practising engineers & designers in today's mobile world.

Results: Instant solutions at your fingertips.



- a small Windows PC program for Gas pipeline hydraulics

- calculate both High pressure (for infra & building distribution pipeline ) and Low pressure (for building internal pipeline) gas pressure systems

- 2 models for high pressure calculations: Weymouth and NFPA

- 1 model for low pressure calculations: NFPA

- options to find flowrate, pipe size and pressure drop

- built-in data, guides, etc

- "save to file" function for printing

- individually selectable SI-IP units


 The selectable SI-IP units available are:


 Parameters High Pressure Low Pressure
 pressurekPa/psi/in.wg/bar  Pa/psi/in.wg/bar
 pipe diameter mm/inmm/in 
 pipe lengthkm/m/mile/ft  m/ft
 pipeline temperature oC/oF
 flowratecmh/cfh  LPS/cmh/cfh




Design Explained 1: High Pressure System 

The Weymouth equation is used for calculating flows and pressure in high pressure gas system. The Weymouth equation does not use Moody friction factor, but uses a pipeline efficiency factor, E. The equation is developed empirically for compressible, turbulent flow with high Reynolds number in long pipelines. The Weymouth equation is one of the oldest and most common equation (as compared to the Panhandle A & B equations) in high pressure gas calculations. The Weymouth equation is considered to be more conservative than the Panhandle A & B equations.


The Weymouth equation in English units is presented as follows (with elevation effects ignored):




It is worth noting that the Weymouth's formula has expressed Moody friction factor as a function of the pipe diameter, i.e. f = 0.008/d1/3.


For NFPA / IFGC formula, refer to NFPA 54 or International Fuel Gas Code.


Design Explained 2: Low Pressure System 

For pressure less than 10 kPa (1.5 psi), the following equation presented in SI units from NFPA / ASHRAE is used to determine gas flow capacity. AGA's International Fuel Gas Code (IFGC) uses the same equation.


 Q = 0.0001d 2.623 [dP/(C*L)]0.541


where  Q = flow rate at 15 oC and 101 kPa (l/s)

           d = inside diameter of pipe (mm)

         dP = pressure drop (Pa)

          C = factor for viscosity, density and temperature

          L = pipe length (m)



Comparisons: Weymouth vs NFPA / IFGC for Lower End of High Pressure System 


Inlet pressure = 5 psi (gauge), Pressure drop = 3.5 psi, Flowrate = 84656 cfh, Gas = Natural Gas, Specific gravity = 0.6, Pipeline temperature = 60 oF, Pipe = smooth wall.


 Pipe Lengh (ft)

Calculated Pipe Diameter (in)

Weymouth formula

 NFPA / IFGC formula


 2.6 2.5


 4.0 4.0


 6.2 6.4




Gas Sizing Example 1: High Pressure System  


Calculate the outlet (downstream) pressue in a 17.5 inch (444.5 mm) natural gas pipeline, 20 miles (32.2 km) long. The gas flow rate is 6,250,000 cfh (176,875 cmh) at a flowing temperature of 70 oF (21.1 oC). The inlet pressure (absolute) is 1014.7 psia (6996.2 kPa) and the gas gravity is 0.6. High Density Polyethylene (HDPE) pipe is used, Assume the pipeline efficiency is 0.98, and compressibility factor is 0.85. Ignore elevation effects.


The following results are computed by pocketGAS program:



Gas Pipeline Hydraulic Calculations
(High Pressure - Weymouth model)
Find Downstream Pressure, P2

upstream pressure, P1 (gauge)1000 psi6894.9 kPa
downstream pressure, P2 (gauge)935.74 psi6451 kPa
mean pressure, Pm (gauge)968.2 psi6675.6 kPa
pressure drop, Pd6.4 %6.4 %
pipe diameter, d17.5 in444.5 mm
pipe length, L20 mile32.2 km
pipeline temp, T70 oF21.1 oC
gas compressibility, z0.850.85
gas sp. gravity, g0.60.6
eff. factor, E0.980.98
FlowRate, Q6250000 cfh176875 cmh
upstream velocity, V113.04 ft/s3.97 m/s
downstream velocity, V213.92 ft/s4.24 m/s
upper limit (erosional) velocity, Vmax52.31 ft/s15.95 m/s


Note: Standard atmospheric conditions used in pocketGas program = 520 oR (15 oC) & 14.7 psi (101.3kPa).


Gas Sizing Example 2: Low Pressure System  

A restaurant serving about 300 persons requires a total gas damand of 1000 cfh (7.8611 l/s) for its cooking equipment. The total pipe length measured from the gas meter to the restaurant kitchen is 60 ft (18.29 m). Natural gas with 0.60 specific gravity is used. The pressure drop from the gas meter to the kitchen shall not exceed 0.3 in. w.g. (74.6 Pa). Determine the required pipe size.


The following results are computed by pocketGAS program:




Gas Pipeline Hydraulic Calculations
(Low Pressure <10kPa - NFPA model)
Find Pipe Diameter, d

 pressure drop, Pd 74.6 Pa0.3 in.wg 
 pipe internal diameter, d 49.7 mm 1.96 in
 pipe length, L18.29 m  60 ft
 Correction factor, Cr 0.610.61 
 FlowRate, Q7.8611 l/s 1000 cfh 



 Gas Sizing Example 3: Medium Pressure System  



Natural Gas:

Medium gas pressure system with pressure available at point D = 60 psi. The 1st regulator is set to deliver 5 psi at the outlet of the regulator. The upstream piping system shall deliver pressure no less than 20 psi at point A to the 1st regulator. Size the gas pipe line from D to A.


Information available:

Building 1 estimated gas demand = 20,000 cfh

Building 2 estimated gas demand = 20,000 cfh

Building 3 estimated gas demand = 30,000 cfh


Pipe length D-C (including fittings) = 250 ft

Pipe length C-B (including fittings) = 200 ft

PIpe length B-A (including fittings) = 200 ft


Working illustrations (by no means this is the only approach):

Allowable pressure drop from D to A = 60-20 = 40 psi.

Total pipe length from D to A = 650 ft.

Allocate pressure losses equally from D to A. Therefore, pressure loss = 40/650 = 0.0615 psi per ft.


(Note: you can distribute the pressure losses any way you wish as long as the sum of the total pressure drop does not exceed the allowable pressure drop.)


Pipe section 

 Upstream pressure 



Downstream pressure



Pipe Size (in.)

using pocketGAS program 

 D-C 6044.625 


 C-B 44.62532.325 


 B-A 32.32520.025



Note: All gas appliances will have their own pressure regulator.






Note: For Compressed Air Pipe Sizing, see CompAir.

Experience yourself the mobility of pocketGas

Price: US $15.90



Download now:

- product detail


OS requirements: Windows XP, Vista, 7, 8, ....     


For Android OS, see                          


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in SI-IP units 


 pocketGas explained






High Pressure calculation (Weymouth)

High Pressure calculation (Weymouth)







Velocity results for High Pressure calculation




 High Pressure calculation (NFPA)



Low Pressure calculation




 Gas Input Converter

(from Btu/h or kW to cfh or cmh)