# Natural Gas Pipe Size Calculator

## Calculate the capacity of natural gas pipe lines

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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)

where

q = natural gas flow capacity (cfh)

h = pressure drop (in Water Column)

l = length of pipe (ft)

k = [d^{5 }/ (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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