Carburetor CFM Calculator

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

Reviewed August 29, 2026 · Calculation methodology · Inputs stay in your browser

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.

Carburetor Sizing Tips

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.