Static, Dynamic and Total Pressure Calculator

Static, dynamic and total pressure

Three pressures are used for a moving fluid. Static pressure is what the fluid exerts on the wall and what an observer moving with the flow would measure. Dynamic pressure is the part due to motion: q = ρ × v² / 2. Their sum is the total pressure, also called stagnation pressure: pt = ps + q. Where the flow is brought to rest in front of an obstacle without loss, the pressure rises to the total pressure.

Measuring velocity with a pitot tube

A pitot tube reads the difference between total and static pressure. That difference equals the dynamic pressure, which gives the velocity: v = √(2 × (pt − ps) / ρ). Air velocity and flow in ventilation ducts are measured this way.

Example

Air at 20 °C (1.204 kg/m³) moving at 20 m/s has a dynamic pressure of 1.204 × 400 / 2 = 240.8 Pa. With a duct static pressure of 250 Pa the total pressure is 490.8 Pa. Going the other way, a pitot reading of 150 Pa means a velocity of √(300 / 1.204) = 15.8 m/s.

Limits

The relations assume incompressible flow. For air, compressibility starts to matter above roughly 100 m/s. The preset densities are for 20 °C at sea level, so enter the density manually for hot air or high altitude. A pitot reading is a point velocity and several readings across the section are needed for the mean.