Fan Brake Horsepower Calculator
Shaft power required to move air against a fan's static pressure.
Enter your values
Enter the airflow in CFM.
Enter the total pressure in in wc.
Enter the fan total efficiency in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Brake horsepower
- 7.26 hp
- Air power
- 4.72 hp
- Motor size (1.15 SF)
- 8.35 hp
- Electrical input at 90% motor eff
- 6.02 kW
Quick answer
Brake horsepower equals CFM times total pressure in inches of water, divided by 6356 times the fan's total efficiency.
BHP = CFM x TP(in wc) / (6356 x eff)
At a glance
| What it does | Shaft power required to move air against a fan's static pressure. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Airflow, Total pressure, Fan total efficiency |
| Main output | Brake horsepower |
| Formula | BHP = CFM x TP(in wc) / (6356 x eff) |
| Cost | Free — no sign-up, no download |
How to use the Fan Brake Horsepower Calculator
- 1Enter the design CFM and total pressure from the fan curve.
- 2Enter the fan's total efficiency at that operating point, from the manufacturer's curve.
- 3Size the motor with a service factor above the calculated brake horsepower.
Inputs explained
- Airflow(CFM)
- Enter the airflow in CFM.
- Total pressure(in wc)
- Enter the total pressure in in wc.
- Fan total efficiency(%)
- Enter the fan total efficiency in %.
Worked example
Using the values the calculator loads with:
Inputs
- Airflow10000 CFM
- Total pressure3.0 in wc
- Fan total efficiency65 %
Results
- Brake horsepower7.26 hp
- Air power4.72 hp
- Motor size (1.15 SF)8.35 hp
- Electrical input at 90% motor eff6.02 kW
Frequently asked questions
Total pressure or static pressure?
Use total pressure (static plus velocity) for true brake horsepower; static-only understates power for high-velocity fans.
Where does 6356 come from?
It converts CFM x inches of water into horsepower (33,000 ft-lb/min per hp with unit conversions).
What do I need to enter into the Fan Brake Horsepower Calculator?
Just 3 values: airflow, total pressure, fan total efficiency. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Fan Brake Horsepower Calculator work out the answer?
Brake horsepower equals CFM times total pressure in inches of water, divided by 6356 times the fan's total efficiency. It applies the formula BHP = CFM x TP(in wc) / (6356 x eff) and shows the working so you can check each step by hand.
Is the Fan Brake Horsepower Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.