Carburetor CFM Calculator
Enter your engine’s displacement, maximum RPM, and volumetric efficiency to calculate the ideal carburetor size in cubic feet per minute (CFM).
What determines carburetor size?
A carburetor needs to flow enough air to match how much an engine can actually breathe at its maximum RPM. Too small and it chokes power; too large and it hurts throttle response and fuel atomization at low speed.
The formula
The standard formula is CFM = (Displacement in cubic inches × Max RPM × Volumetric Efficiency) ÷ 3456. Volumetric efficiency (VE) reflects how effectively the engine actually fills its cylinders each cycle compared to a theoretical 100%, typically 80-90% for a stock engine and higher for a well-tuned performance build.
This calculates the theoretical ideal CFM for peak RPM; real-world carburetor selection also considers driving style, intended RPM range, and available carburetor sizes. This calculator is for general automotive reference and educational purposes.