Enter the pressure drop, length of pipe, and diameter of pipe into the calculator to determine the gas piping size by cubic feet per hour.

Gas Piping Size Formula

The following formula is used to calculate the flow rate of natural gas through a pipe of a certain size: 

q = 3550 * [d^5 / (1+3.6/d + .03*d)]^{1/2} * (h / (L*SG))^{1/2}
  • Where q is the volumetric flow rate (cfh – cubic feet per hour)
  • d is the diameter of the tube (inches)
  • h is the pressure drop
  • L is the length of the tube (ft)
  • SQ is the specific gravity (.60 average)

What is a gas pipe size?

The correct gas pipe size depends on the diameter, length, and pressure drop of the pipe. It also depends on the specific gravity of the gas moving through the pipe.

How to calculate gas pipe flow rate?

Example Problem:

The following example problem outlines how to calculate the gas pipe flow rate of natural gas.

First, determine the diameter of the pipe. In this example, the diameter is measured to be 5 inches.

Next, measure the pressure drop across the tube. The value of this for this example is 3.

Next, measure the length of the tube. This yields a length of 50 feet.

Finally, using the information above and the specific gravity of the gas, calculate the flow rate using the formula:

q = 3,550 * [d^5 / (1+3.6/d + .03*d)]^1/2 * (h / (L*SG))^1/2

q = 3,550 * [5^5 / (1+3.6/5 + .03*5)]^1/2 * (3 / (50*.60))^1/2

q = 148,312