Motor HP to CFM Calculator
Estimate achievable CFM from available motor horsepower.
Enter your values
Enter the motor horsepower in hp.
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.
- Achievable airflow
- 9,534 CFM
- At half load HP (spare capacity)
- 4,767 CFM
- Air power delivered
- 3 hp
Quick answer
Achievable CFM equals motor horsepower times 6356 times fan efficiency, divided by the total pressure.
CFM = HP x 6356 x eff / TP
At a glance
| What it does | Estimate achievable CFM from available motor horsepower. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Motor horsepower, Total pressure, Fan total efficiency |
| Main output | Achievable airflow |
| Formula | CFM = HP x 6356 x eff / TP |
| Cost | Free — no sign-up, no download |
How to use the Motor HP to CFM Calculator
- 1Enter the motor's rated horsepower.
- 2Enter the total pressure the system needs to overcome.
- 3Enter the expected fan efficiency, then read the CFM that horsepower can realistically deliver.
Inputs explained
- Motor horsepower(hp)
- Enter the motor horsepower in hp.
- 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
- Motor horsepower5 hp
- Total pressure2.0 in wc
- Fan total efficiency60 %
Results
- Achievable airflow9,534 CFM
- At half load HP (spare capacity)4,767 CFM
- Air power delivered3 hp
Frequently asked questions
Is this exact?
It is an estimate — actual CFM depends on the specific fan curve and drive losses.
What if pressure varies with flow?
Iterate: check the resulting CFM against the system curve pressure at that flow and recompute.
What do I need to enter into the Motor HP to CFM Calculator?
Just 3 values: motor horsepower, 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 Motor HP to CFM Calculator work out the answer?
Achievable CFM equals motor horsepower times 6356 times fan efficiency, divided by the total pressure. It applies the formula CFM = HP x 6356 x eff / TP and shows the working so you can check each step by hand.
Is the Motor HP to CFM 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.