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Calcimator

Pneumatic Tubing Calculator

Size pneumatic tubing by calculating velocity, pressure drop, burst pressure (Barlow's formula), and recommended OD for air systems.

About this calculator

This calculator checks two independent things about a run of pneumatic tubing: whether it's strong enough to safely hold the working pressure, and whether it's sized large enough to deliver the required airflow without excessive velocity or pressure loss. Burst pressure is found from Barlow's formula (Burst = 2 × tensile strength × wall thickness / OD), using tensile strength values keyed to the selected material — nylon (8,000 psi), polyurethane (5,000 psi), copper (32,000 psi), or steel (60,000 psi) — and the reported maximum working pressure divides that burst figure by a fixed 4:1 safety factor, standard practice for pneumatic tubing. On the flow side, actual compressed-air flow (ACFM) is derived from the standard SCFM input using the compression ratio at line pressure, then divided by the tube's cross-sectional area to get velocity — this calculator flags velocities above 30 ft/s as a caution, since excessive velocity wastes energy and increases noise and erosion.

Pressure drop uses a simplified empirical (Harris-type) formula that scales linearly with tube length, with flow rate raised to a 1.85 exponent, and inversely with the fifth power of inner diameter, meaning a modest reduction in ID causes a dramatic increase in pressure loss — this is the single most important intuition for tubing sizing. Fittings are approximated as 2 ft of equivalent straight length each, a rough industry rule of thumb rather than a precise value; actual equivalent lengths vary considerably by fitting type and should be checked against manufacturer data for critical runs.

Inputs

psi
ft
psi
in
in

Results

Air velocity (ft/s)

31.3

Total pressure drop (PSI)329.82
Burst pressure (PSI)2,080
Max working pressure (PSI)520
Tube ID (in)0.37
Recommended tube OD (in)0.63
Actual CFM (compressed)1.4
Straight-run drop (PSI)249.87
Velocity OkNo
Drop OkNo
How to Use This Calculator
  1. Enter Air flow (SCFM), Line pressure (PSI), and Tube run length (ft).
  2. Set Allowable pressure drop (PSI), Tube OD (in), and Wall thickness (in).
  3. Adjust Material (1=nylon, 2=PU, 3=copper, 4=steel), Number of fittings as needed.
  4. Review the Air velocity (ft/s) result.
  5. Use Total pressure drop (PSI) and Burst pressure (PSI) to inform your decision.

How the result changes with Tube OD (in)

Tube OD (in)Air velocity (ft/s)
0.25297.9
0.3871.5
0.7511.2
1.253.4

What each input means

Air flow (SCFM)
Standard cubic feet per minute of air demand.
Line pressure (PSI)
Working pressure in the pneumatic line.
Tube run length (ft)
Total straight-line tube length in feet.
Allowable pressure drop (PSI)
Maximum acceptable pressure loss in the run.
Tube OD (in)
Outside diameter of the tubing.
Wall thickness (in)
Tube wall thickness.
Material (1=nylon, 2=PU, 3=copper, 4=steel)
Tube material affects burst pressure rating.
Number of fittings
Push-to-connect or compression fittings in the run.

What each result means

Air velocity (ft/s)
Compressed air velocity in the tube (keep <30 ft/s for mains, <60 for branches).
Total pressure drop (PSI)
Combined pressure loss from tube length and fittings.
Burst pressure (PSI)
Calculated burst pressure from Barlow's formula.
Max working pressure (PSI)
Burst pressure divided by 4:1 safety factor.
Tube ID (in)
Calculated inner diameter (OD minus 2× wall thickness).
Recommended tube OD (in)
Next standard tube OD that keeps velocity under 25 ft/s.
Actual CFM (compressed)
Actual volume flow at operating pressure.
Straight-run drop (PSI)
Pressure drop from tubing length only (excluding fittings).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Air flow (SCFM) = 10, Line pressure (PSI) = 90, Tube run length (ft) = 25, Allowable pressure drop (PSI) = 3 = 8 input(s) provided
  2. Calculate Air velocity
    Air velocity = velocityFtMin / 60
    31.3 = 31.3
  3. Calculate Total pressure drop
    Total pressure drop = straightDrop + fittingDrop
    329.82 = 329.82
  4. Calculate Burst pressure
    Burst pressure = (2 * tensileStrength * wallThickness) / tubeOd
    2080 = 2080

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does a small reduction in tube ID cause such a big jump in pressure drop?

The pressure-drop formula divides by inner diameter raised to the fifth power (d^5), so even a modest ID reduction compounds dramatically — dropping ID by roughly 20% (a factor of 0.8) increases the pressure-drop term by about 1/0.8^5, or roughly 3x. This is why the explainer calls diameter the single most important variable in tubing sizing: length and flow rate matter, but ID dominates.

How is Burst Pressure calculated, and why does switching materials change it so much?

Burst pressure uses Barlow's formula — 2 × tensile strength × wall thickness ÷ outer diameter — with tensile strength pulled from a fixed lookup keyed to the selected material: nylon at 8,000 psi, polyurethane at 5,000 psi, copper at 32,000 psi, or steel at 60,000 psi. Because tensile strength enters the formula as a direct multiplier, switching from polyurethane to steel at the same wall thickness and OD raises burst pressure by roughly 12x.

What's the difference between the Tube ID input relationship and the recommended OD output?

You enter Tube OD and Wall Thickness directly, and the calculator derives Tube ID by subtracting twice the wall thickness from the OD. Recommended Tube OD is a separate, independent result: it back-calculates the ID needed to keep velocity at or below a 25 ft/s target for your actual airflow, then matches that to the next standard tube OD size — it does not just re-list your input.

Why is Max Working Pressure always exactly one quarter of Burst Pressure?

The calculator applies a fixed 4:1 safety factor, standard pneumatic tubing practice, by dividing the Barlow's-formula burst pressure directly by 4 with no other inputs affecting that ratio. If your working pressure input exceeds this Max Working Pressure result, the tube's wall thickness or material should be increased rather than accepting the reduced margin.

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