Calculate fan wind speed in mph, km/h or m/s from the fan’s airflow in CFM and its outlet size, or solve for the airflow or outlet diameter you need.

The fan’s rated airflow, usually listed on the box or spec sheet in CFM.

Free area and pressure estimate
100% means the full geometric opening. Enter the known open fraction for grille or hub blockage.

Blank omits dynamic pressure. Enter actual density for a uniform-profile estimate; this is not fan static pressure.

Related Calculators

Fan Outlet Wind Speed Formula

The calculator finds average outlet air speed from actual volumetric airflow and effective open area. Blade tip speed and downstream throw are different quantities:

V = Q / Aโ‚‘ffective; Aโ‚‘ffective = Agross ร— f

Variables:

  • V is average outlet air speed (m/s when Q is mยณ/s and area is mยฒ)
  • Q is actual volumetric airflow at the outlet conditions
  • A_gross is the geometric outlet area; circular area = ฯ€ ร— (D/2)ยฒ and rectangular area = width ร— height
  • f is the effective free-area percentage divided by100; A_effective is the resulting open area

Calculate gross area, multiply by the known free-area fraction, then divide actual volumetric airflow by effective area. The reverse solves use Q = V ร— A_effective and D =2 ร— โˆš[Q / (ฯ€ ร— V ร— f)] for a circular outlet.

What is Fan Outlet Wind Speed?

Outlet wind speed here is the area-average air velocity normal to the effective opening. It is not the tangential speed of the rotating blade tip and does not predict downstream speed. Grilles, hubs, nonuniform profiles, fan geometry and system resistance affect real conditions. An optional supplied air density adds a uniform-profile dynamic-pressure estimate (0.5 ร— density ร— speedยฒ), not a fan static-pressure prediction.

How to Calculate Average Outlet Wind Speed?

The following steps match the average outlet-speed mode; airflow and circular-diameter inverse modes use the same relation.

  1. First, obtain actual outlet airflow and choose its unit. Use actual-volume flow corresponding to the measured outlet conditions.
  2. Choose circular or rectangular outlet geometry and enter its inside dimensions.
  3. Set the effective free-area percentage if the opening is obstructed;100% means the full geometric area.
  4. Calculate V = Q / A_effective in consistent units and choose m/s, ft/min, mph or km/h for display.
  5. Check the result with the calculator. Changing free area or units retains the previous result until Calculate is selected.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Hypothetical circular outlet inside diameter =16 inches; effective free area =100%.

Actual airflow =2000 CFM. Effective area โ‰ˆ0.129717 mยฒ; average outlet speed โ‰ˆ7.276564 m/s.