Motor HP to CFM Calculator
Estimate achievable CFM from available motor horsepower.
Enter your values
ⓘ Live results
Results
- 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
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.
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.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.