How To Calculate the Size of Carburetor Needed in CFM

Optimize performance with a correctly sized carburetor

How To Calculate Size of Carburetor Needed in CFM

This carburetor calculator is designed to give the engine’s air intake volume requirements in Cubic Feet per Minute.

  1. Enter the engine displacement and the anticipated maximum safe engine RPMs (typically known as redline).
  2. Click ‘Calculate’ – The value will be returned in Cubic Feet per Minute (CFM) required based on the entry values you have made.

This calculator will show you the CFM at the maximum RPM entered, if your engine is capable of turning 7,500 RPM but you shift at 5,500, then use the shift point, not the maximum RPM.

Editor’s Note: Big Stall Converters, huge gears, and very light cars are outside the scope of this calculator and a competent carburetor professional should be consulted.

Enter Maximum Engine RPM

Engine Size in Cubic Inches

Stock Engine VE (75-85% VE)


Mild Build VE (85-90% VE)


Racing Engine VE (90-100% VE)


Volumetric Efficiency: Most factory engines are a compromise between economy, efficiency, reliability, and performance; about 80% at redline.

Engines that have been tuned for improved performance or have a stronger performance camshaft and valve combination may have up to 90%.

A competition roller cam and valve combination may yield 95% while blowers often achieve up to 115%.)

These high-performance situations are beyond the scope of this calculator.