Calculate compressed air velocity from standard or actual flow, pipe diameter, pressure, and temperature, with results in ft/s, m/s, and ft/min.
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Compressed Air Velocity Formula
The calculator uses one of three formulas depending on the inputs you have.
Mode 1: SCFM and pipe size. Convert standard flow to actual flow at line conditions, then divide by pipe area.
V = [SCFM × (14.696 / P_abs) × (T / 527.67)] / A / 60
Mode 2: Actual flow and pipe size.
V = Q_actual / A / 60
Mode 3: Velocity pressure.
V = sqrt(2 × ΔP / ρ), where ρ = P_abs / (R_air × T)
- V = air velocity (ft/s or m/s)
- SCFM = standard cubic feet per minute (at 14.696 psia, 68°F)
- Q_actual = actual volumetric flow at line conditions (CFM)
- P_abs = absolute line pressure (psia or Pa)
- T = absolute line temperature (°R or K)
- A = pipe cross-sectional area = π × D² / 4 (ft²)
- ΔP = velocity pressure (Pa)
- ρ = air density (kg/m³)
- R_air = 287.05 J/(kg·K)
Standard conditions are 14.696 psia and 68°F. Air is treated as an ideal gas, which is accurate enough for shop air below about 200 psig.
Reference Tables
Use these tables to sanity-check your input and your result.
| Velocity (ft/s) | Typical use | Notes |
|---|---|---|
| Under 15 | Oversized header | Low drop, higher pipe cost. |
| 20–30 | Main headers | Common design target. |
| 30–50 | Branch lines, drops | Acceptable for shorter runs. |
| Over 50 | Undersized pipe | Noise, drop, moisture carryover. |
| Sch 40 pipe | ID (in) | SCFM at ~30 ft/s, 100 psig |
|---|---|---|
| 1/2 in | 0.622 | ~26 |
| 3/4 in | 0.824 | ~46 |
| 1 in | 1.049 | ~75 |
| 1 1/2 in | 1.610 | ~177 |
| 2 in | 2.067 | ~292 |
| 3 in | 3.068 | ~643 |
| 4 in | 4.026 | ~1,107 |
Worked Example
You have 100 SCFM flowing through 1 in Sch 40 pipe (ID 1.049 in) at 100 psig and 68°F.
- Pipe area: A = π × (1.049/12)² / 4 = 0.006 ft².
- Pressure ratio: 14.696 / 114.696 = 0.128.
- Actual flow: 100 × 0.128 × 1 = 12.8 CFM.
- Velocity: 12.8 / 0.006 / 60 = ~35.6 ft/s.
That sits in the branch-line range. Stepping up to 1 1/4 in pipe drops velocity below 22 ft/s, which is closer to the main-header target.
Why velocity matters
High velocity in compressed air piping causes pressure drop, turbulence at fittings, and lifts condensed moisture past drip legs. Sizing pipe for 20–30 ft/s on mains keeps drop below roughly 1 psi per 100 ft for typical shop layouts.
