CFM to Horsepower Calculator
Estimate horsepower from airflow in CFM, and size a carburetor or intake.
Because an engine's power is limited by how much air it can flow, airflow in CFM gives a good estimate of supported horsepower. This calculator helps you match a carburetor or intake to a power target.
CFM to HP Formula
This estimates the horsepower the induction can support, not what the engine will necessarily make — actual power also needs matching displacement, compression, cam, fuel, and tune. It's most useful for sizing carbs, throttle bodies, and intakes.
How to Use This Calculator
- Enter airflow in CFM (e.g. carburetor rating).
- Read the supported horsepower.
Worked Example
Why Airflow Limits Horsepower
An engine is fundamentally an air pump — it can only burn as much fuel as it has oxygen to burn, and oxygen comes from airflow. That's why CFM (cubic feet per minute) of induction airflow sets a ceiling on power. The ~1.6 HP-per-CFM rule of thumb estimates how much horsepower a given carburetor, throttle body, or intake can support, which is why airflow is the first thing engine builders size against a power goal.
Supported Power vs Actual Power
This is a ceiling, not a promise. An intake that can flow enough for 1,200 HP won't make 1,200 HP unless displacement, compression, camshaft, fuel system, and tune all match. Oversizing a carb for a small engine actually hurts low-end response. Use the figure to avoid an induction restriction, then build the rest of the engine to use that airflow.
Supported HP by Airflow (NA)
| Airflow (CFM) | Supported HP | Typical use |
|---|---|---|
| 390 | ~625 | Small-block street |
| 600 | ~960 | Performance street/strip |
| 750 | ~1,200 | Big-block / race |
| 950 | ~1,520 | Large race engine |
Frequently Asked Questions
A naturally aspirated engine supports roughly 1.6 horsepower per CFM of airflow, so multiply CFM by about 1.6 for a rough capacity estimate.
No. Oversizing the carb or intake beyond the engine's airflow needs hurts throttle response and low-end power without adding top-end.
It estimates the horsepower the airflow (e.g. a carburetor's CFM rating) can support. The engine must also be built to use it.
No. Forced induction supplies far more air per unit of displacement, so the naturally aspirated CFM-to-HP rule doesn't apply directly.
Estimate airflow from displacement, RPM, and volumetric efficiency, then choose induction that meets or slightly exceeds that figure.