Pitot differential-pressure velocity

Convert a local total-minus-static pressure reading to air velocity using measured density and probe coefficient.

How this calculation works

A Pitot-static reading provides the difference between local total and static pressure. Enter that differential pressure, the air density for the measurement condition and the probe's velocity calibration coefficient. The calculator takes the square root of twice the pressure difference divided by density, then multiplies by the coefficient. A pressure reading alone therefore does not determine velocity unless the density and probe basis are appropriate. The result is a local velocity at the probe location. Estimating duct flow requires a representative cross-sectional velocity distribution and area, not simply one convenient reading. The relation assumes correctly aligned, low-speed incompressible flow. Reverse flow, high-speed compressibility and static-pressure-only readings are outside its scope, while low differential readings deserve particular attention to sensor zero and resolution.

Inputs and units

Total minus static pressure (Pa)
Air density (kg/m³)
Probe velocity coefficient (fraction)

Method and formula

Velocity = Cprobe sqrt(2 Δp/ρ), with Δp in Pa, density in kg/m³, and Cprobe a dimensionless calibration factor.

Worked example

Example inputs

Total minus static pressure: 60 Pa
Air density: 1.2 kg/m³
Probe velocity coefficient: 1 fraction

Calculation steps

Twice pressure divided by density = 2 × 60 / 1.2 = 100 m²/s².
Local air velocity = 1 × √100 = 10 m/s.

Example results

Local air velocity: 10 m/s

Assumptions

Low-speed incompressible air and a correctly aligned calibrated probe.

Limitations

One local velocity is not the cross-sectional mean or total airflow.
Does not handle reverse flow, compressible high-speed flow or static-pressure-only readings.
Preliminary educational check; verify inputs and equipment data before design or operation.

Sources

NASA Glenn: Pitot-static tube: Bernoulli relation between total pressure, static pressure, density and velocity
TSI: Traversing a Duct, application note TSI-106: Pages 1–3: average local velocities, multiply by area; actual traverses need appropriate measurement layouts