Pitot Tube Calculator

Calculate flow velocity from a pitot tube’s differential pressure or manometer reading, using typical air or water density or your own, plus duct CFM.

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Calculator Functions

The calculator turns a pitot tube reading into flow velocity in m/s, ft/min and mph. Select a function to open it in the calculator.

Function	Use it when	You enter
Differential pressure	A gauge gives you the pressure difference directly	Total minus static pressure
Velocity head in flowing fluid	The flowing fluid itself rises in the tube	Vertical height difference
U-tube manometer	A denser liquid in a U-tube shows the difference	Vertical height difference and manometer liquid density
Traverse average	You took readings across a duct	2–200 equal-area pressure readings
Centerline approximation	You can only take one reading and a rough average is enough	One pressure reading at the duct center

Every function also asks for the flowing fluid: air at 20 °C, air at 15 °C, water at 20 °C or a custom density. Optional settings add a pitot coefficient and a flow area or duct size, which also gives volumetric flow in m³/s and CFM.

Pitot Tube Formulas

Differential pressure

Your reading is Δp, so the formula above applies directly.

Velocity head in flowing fluid

Δh is the vertical height difference in the flowing fluid, and g = 9.80665 m/s².

U-tube manometer

Δh is the height difference on the manometer liquid, which must be denser than the flowing fluid. This assumes the pressure taps are at the same level.

Traverse average

Each reading is converted to velocity first, because averaging the pressures and then converting gives a different answer. Readings should represent equal areas of the duct, and the calculator does not choose the positions.

Centerline approximation

This gives a rough duct average from one reading at the center.

Volumetric flow

For a round duct, A = π × D² ÷ 4. For a rectangular duct, A = width × height. A single reading only works here if it represents the average velocity across the duct.

Limits of This Estimate

• Assumes steady, incompressible flow. Very low speeds are hard to measure accurately, and the equation does not hold at supersonic speeds [1]. The calculator warns you below 5 Pa.
• Preset densities are for 1 atm. Use a custom density for other fluids, temperatures or altitudes.
• The centerline function is a shortcut. One manufacturer quotes ±5% for it and ±2% for a careful traverse [4].

Sources