Carburetor CFM Calculator – Find Recommended Carburetor Size

Enter the engine size, max RPM, and volumetric efficiency to calculate the recommended carburetor CFM.

Carburetor Size:

Learn how we calculated this below

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How to Calculate the Carburetor Size for an Engine

Equipping your engine with the right size carburetor is critical to maximize the performance of the motor. Too small of a carburetor and the engine will be starved of fuel, too large and it will be choked.

Carburetors are sized by the amount of airflow they can handle in cubic feet per minute, or CFM.

So, what size carburetor do you need then? There’s a simple formula to calculate just the right size of carburetor for your engine.

carburetor size = engine size × max rpm × efficiency ÷ 3456

The engine size is the displacement in cubic inches. If you know the displacement in liters, try converting using our liters to cubic inches calculator. Try our engine displacement calculator to find the size of your engine

The max RPM is the maximum speed of the engine in revolutions per minute.

The efficiency is the volumetric efficiency of the motor. Most engines have a volumetric efficiency of about 85%, or .85. It’s common to see efficiency values of 70-80% up to 95-110% for race engines.

For example, let’s find the recommended carburetor size for an engine with a displacement of 302 cubic inches, a max speed of 7,500 RPM, and 80% volumetric efficiency.

carburetor size = 302 × 7,500 × .8 ÷ 3456
carburetor size = 524.31 CFM

You might also like our engine horsepower and compression ratio calculators.