Carburetor size calculator

Four-stroke airflow (CFM) = cubic inches × rpm × volumetric efficiency ÷ (100 × 3456).

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Engine displacement (cubic inches)

Maximum engine speed (rpm)

More inputs and assumptions

Volumetric efficiency (%)

Answer

…

Four-stroke airflow (CFM) = cubic inches × rpm × volumetric efficiency ÷ (100 × 3456).

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Precision and calculation record

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Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

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Formula and assumptions

The 3456 divisor is 1728 cubic inches per cubic foot times two crankshaft revolutions per intake cycle. Volumetric efficiency is your assumption, not measured by this tool. Airflow is not a carburetor fitment or jetting recommendation; induction, pressure drop and operating conditions matter.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-29

Using Carburetor size calculator

Four-stroke airflow (CFM) = cubic inches × rpm × volumetric efficiency ÷ (100 × 3456).

Next: Engine displacement calculator

Next: Engine horsepower calculator

A worked example

For engine displacement (cubic inches) = 350, maximum engine speed (rpm) = 6000, volumetric efficiency (%) = 85, estimated airflow (cfm) = 516.

Before you use the result

Example results for engine displacement (cubic inches)

These examples use Maximum engine speed (rpm): 6000; Volumetric efficiency (%): 85. They are reference calculations, not recommended settings.

Engine displacement (cubic inches)	Estimated airflow (CFM)
175	258
350	516
700	1033

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