How do you calculate face velocity at a fan inlet or outlet?

Divide airflow in CFM by the open area in square feet to get raw velocity, then multiply by the effective open-area factor. With 12,000 CFM through 8 sq ft at 92% effective area, raw velocity is 1,500 ft/min and effective velocity is 1,380 ft/min.

What is a good outlet velocity for an industrial fan?

It depends on the application: low-noise comfort ventilation often targets under 1,500–2,000 ft/min, while process and material-handling systems run much higher. The 1,380 ft/min here is moderate and quiet for a general-purpose outlet.

Why use an effective open-area factor?

Inlet screens, bird guards, bellmouths, and frame webs block part of the nominal opening. The 92% factor here means 8% of the face is obstructed, so true velocity through the open holes is 1,380 ft/min rather than the raw 1,500.

How does velocity relate to pressure loss?

Dynamic pressure rises with the square of velocity, so a 10% higher face velocity costs roughly 21% more velocity-pressure loss. Keeping effective velocity in check directly trims fan energy and noise.

CFM vs FPM — what's the difference?

CFM is volume flow (cubic feet per minute); FPM is velocity (feet per minute). Velocity equals CFM divided by area, which is exactly what this calculator does before applying the open-area correction.

Does this give average or peak velocity?

Average. Real face velocity profiles are non-uniform, peaking near the fan throat; multiply by 1.2–1.5 for a rough peak estimate when checking screen erosion or noise.

Industrial Fans, Blowers & Air Movement Equipment calculator

Inlet/Outlet Velocity Calculator

Inlet/Outlet Velocity converts a fan's volumetric airflow into face velocity at the inlet or outlet, then corrects it for the effective open area lost to guards, screens, and frame blockage. Fan selection engineers, ventilation designers, and balancing technicians rely on it because face velocity drives system pressure loss, noise, screen erosion, and whether a hood actually captures contaminant. Computing both the raw velocity (CFM divided by area) and the effective velocity after the open-area factor keeps you honest about what the air is really doing at the opening, not what a clean-area calculation suggests.

What this calculator does

Estimate effective inlet or outlet air velocity from airflow, opening area, and efficiency or blockage allowance.
Use it when checking inlet velocity, outlet velocity, duct connection sizing, discharge speed, or dust collection transport assumptions.
It divides airflow by opening area for a raw face velocity, then multiplies by an effective open-area factor to account for screens, guards, and frame blockage.

Formula used

Raw inlet or outlet velocity = airflow through opening ÷ inlet or outlet open area
Effective inlet or outlet velocity = raw velocity × open-area efficiency allowance

Inputs explained

Airflow through the opening:
Inlet or outlet free open area:
Effective open-area factor:

How to use the result

Use it when sizing an inlet, outlet, hood face, or duct transition and you need the real velocity at the plane of the opening.
It assumes uniform velocity across the face; in reality flow concentrates near the fan throat and separates at corners, so localized velocities can run well above the average.

Current U.S. benchmarks

Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate face velocity at a fan inlet or outlet? Divide airflow in CFM by the open area in square feet to get raw velocity, then multiply by the effective open-area factor. With 12,000 CFM through 8 sq ft at 92% effective area, raw velocity is 1,500 ft/min and effective velocity is 1,380 ft/min.
What is a good outlet velocity for an industrial fan? It depends on the application: low-noise comfort ventilation often targets under 1,500–2,000 ft/min, while process and material-handling systems run much higher. The 1,380 ft/min here is moderate and quiet for a general-purpose outlet.
Why use an effective open-area factor? Inlet screens, bird guards, bellmouths, and frame webs block part of the nominal opening. The 92% factor here means 8% of the face is obstructed, so true velocity through the open holes is 1,380 ft/min rather than the raw 1,500.
How does velocity relate to pressure loss? Dynamic pressure rises with the square of velocity, so a 10% higher face velocity costs roughly 21% more velocity-pressure loss. Keeping effective velocity in check directly trims fan energy and noise.
CFM vs FPM — what's the difference? CFM is volume flow (cubic feet per minute); FPM is velocity (feet per minute). Velocity equals CFM divided by area, which is exactly what this calculator does before applying the open-area correction.

Last reviewed 2026-05-12.