Carburetor CFM Calculator

Calculate the necessary Cubic Feet per Minute (CFM) rating for your carburetor based on engine displacement and RPM.

Engine Displacement Enter your engine's displacement.

Maximum RPM Enter the maximum RPM your engine will reach.

Volumetric Efficiency (%) Standard street engines: 80-85%, Modified engines: 85-95%, Race engines: 95-110%

Engine Type Select your engine cycle type.

The basic CFM formula is: (Engine Displacement × Maximum RPM × Volumetric Efficiency) ÷ 3456
For 2-stroke engines, the formula is modified since they fire every revolution.
Volumetric efficiency varies based on engine modifications - stock engines are typically 80-85%.
It's generally better to have a slightly larger carburetor than one that's too small.
Common carburetor sizes are 500, 600, 650, 750, 800, 850, and 1050 CFM.
Street engines typically perform best with a carburetor that flows slightly less than the theoretical maximum.