Pitot Tube Velocity Calculator
Convert the dynamic pressure from a pitot or pitot static tube into velocity, and into flow rate for a duct or pipe of known size.
- v = C × √(2ΔP ÷ ρ) = 1 × √(2 × 250 ÷ 1.2) = 20.41 m/s
- Q = v × mean ratio × A = 14,429 m³/h
Pitot Tube Formula
Q = vmean × A
ΔP is the difference between total and static pressure, ρ the fluid density and C the probe coefficient (close to 1.0 for standard pitot static tubes). Use a traverse, or a mean to point ratio, to convert a single point reading to average velocity.
Worked example
In air (1.2 kg/m³) a dynamic pressure of 250 Pa gives v = √(2 × 250 ÷ 1.2) = 20.4 m/s. In a 500 mm duct with that as the mean velocity, Q = 14,430 m³/h.
Frequently Asked Questions
How does a pitot tube measure velocity?
The facing port senses total pressure and the side ports static pressure. Their difference, the dynamic pressure, equals ½ρv².
What is a typical pitot coefficient?
About 1.0 for ellipsoidal nose pitot static tubes and 0.84 for S type (Stauscheibe) probes.
How do I get average velocity in a duct?
Do a traverse at several points across the duct (for example log Tchebycheff positions) and average the velocities, not the pressures.
Learn more on the blog
What factors affect the stability of flow meter readings?
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article