Pipe Sizing (Compressed Air) Calculator

Pipe diameter from CFM and acceptable pressure drop.

Air flow (CFM free air)

Pipe run length (ft)

Operating pressure (psig)

Max pressure drop (psi)

Fittings equivalent length

Tab to move between fields

Recommended pipe size (NPS)

0.5

Actual pipe ID (inches)0.62

Minimum calculated ID (in)0.55

Actual pressure drop (psi)1.59

Air velocity (ft/s)101.2

Velocity rating3

Equivalent length (ft)300

How to Use This Calculator

Enter the required flow rate in CFM and system operating pressure in PSI.
Set the pipe run length in feet and number of fittings (add equivalent lengths for elbows and tees).
Set the allowable pressure drop in PSI for the distribution run.
Review the recommended pipe inside diameter and nearest standard pipe size.
Verify the calculated velocity stays below 20-30 FPS to avoid excessive turbulence.

What each input means

Air flow (CFM free air): Flow rate in cubic feet per minute at atmospheric pressure (free air delivery).
Pipe run length (ft): Straight-line length of the pipe run from header to point of use.
Operating pressure (psig): System operating pressure in gauge PSI.
Max pressure drop (psi): Maximum acceptable pressure drop across this pipe run. Best practice: < 1 psi per run, < 3% of system pressure total.
Fittings equivalent length: Extra length to add for elbows, tees, valves, etc. 50% is typical for a moderately complex run.

Recommended pipe size (NPS): Nominal Pipe Size (inches) — the standard designation for ordering pipe.
Actual pipe ID (inches): Inside diameter of the selected Schedule 40 pipe.
Minimum calculated ID (in): Minimum inside diameter to meet pressure drop requirement.
Actual pressure drop (psi): Estimated pressure drop with the selected standard pipe size.
Air velocity (ft/s): Air velocity in the pipe. Keep below 20 ft/s for headers, 30 ft/s for branch lines.
Velocity rating: 1 = Good (< 20 ft/s), 2 = Acceptable (20–30 ft/s), 3 = Too high (> 30 ft/s, risk of noise/erosion).
Equivalent length (ft): Total equivalent pipe length including fittings allowance.

Identify Input Parameters
4 parameters
Air flow (CFM free air) = 100, Pipe run length (ft) = 200, Operating pressure (psig) = 100, Max pressure drop (psi) = 3 = 5 input(s) provided
Calculate Recommended pipe size
Recommended pipe size
0.5 = 0.5
Calculate Actual pipe ID
Actual pipe ID
0.622 = 0.622
Calculate Minimum calculated ID
Minimum calculated ID = C * pow(numerator / max(0.001, denominator), 0.2)
0.55 = 0.55