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Calculation Machine

Velocity Pressure Calculator

Velocity pressure and equivalent velocity from a pitot reading.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Velocity
2,003 FPM
Velocity
10.2 m/s
Velocity pressure entered
0.25 in wc

Quick answer

Velocity in feet per minute equals 4005 times the square root of velocity pressure in inches of water at standard air density.

The formula

V = 4005 x sqrt(VP)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Velocity pressure0.25 in wc

Result

  • Velocity2,003 FPM
  • Velocity10.2 m/s
  • Velocity pressure entered0.25 in wc

How to use the Velocity Pressure Calculator

  1. 1Read velocity pressure from a pitot tube and manometer or micromanometer.
  2. 2Enter the value here to get the equivalent air velocity.
  3. 3Multiply velocity by duct area to get CFM.

Frequently asked questions

Does air temperature matter?

Yes — the 4005 constant assumes standard air; correct for density at high temperature or altitude.

What if I measure velocity directly?

Use it directly; VP = (V/4005)^2 converts the other way if needed.

About this calculator