Natural Gas - Pipe Sizing Calculator

Calculate the capacities and dimensions of natural gas pipe lines

The capacity of a low pressure natural gas (less than 1 psi, 6.9 kPa) pipe line with a small pressure drop can be calculated with the Spitzglass formula

q = 3550 k ( h / l SG)1/2         (1)


q = natural gas flow capacity (cfh)

h = pressure drop (in Water Column)

l = length of pipe (ft)

k = [d5 / (1 + 3.6 / d + 0.03 d)]1/2

d = inside diameter pipe (in)

SG = specific gravity

For natural gas the nominal BTU/cf varies from about 900 to 1100 BTU/cf. In general it is common to set

  • 1 Cubic Foot (CF) = approx 1,000 BTUs
  • 1 CFH = 1 MBH

The specific gravity of natural gas varies from 0.55 to 1.0.

The downstream pressure in a houseline after the meter/regulator is in general in the range of 7 to 11 inches Water Column, or about 1/4 psi.

Example - Natural Gas Pipe Capacity

The capacity of a 100 ft natural gas pipe with a nominal diameter 0.5 inches (actual ID 0.622 in) and 0.5 inches WC pressure drop can be calculated as

k = [((0.622 in))5/(1 + 3.6 / (0.622 in) + 0.03 (0.622 in))]1/2

= 0.117

q = 3550 0.117 ((0.5 in) / (100 ft) 0.60 )1/2

= 37.9 (cfh)

Specific gravity of natural gas is set to 0.60.

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Natural gas pipe calculator

pipe inside diameter - d (in)

pressure drop - h (in WC)

pipe length - l (ft)

specific gravity - SG

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