Range Hood CFM Calculator

For a gas cooktop, divide the total burner output by 100, so a 40,000 BTU range needs about 400 CFM. For an electric or induction cooktop, use about 10 CFM per inch of cooktop width, or 100 CFM per linear foot, so a 30 inch range needs about 300 CFM. These are the sizing rules from the Home Ventilation Institute and the National Kitchen and Bath Association. Heavy or frequent high-heat cooking pushes you toward the upper end.

Gas burners are rated directly in BTU per hour, so the heat and combustion byproducts you need to capture scale with that number, which is why the rule is 1 CFM per 100 BTU. Electric and induction cooktops are not rated in BTU in a comparable way, so the industry sizes them by the cooking surface width instead, at roughly 10 CFM per inch. Both methods aim to clear the rising plume of heat, steam, and grease over the burners.

Yes. An island or peninsula cooktop has no surrounding walls or backsplash to contain the cooking plume, so air drifts out the open sides before the hood can catch it. The common guideline raises the rate from 100 CFM per linear foot against a wall to 150 CFM per linear foot over an island, which is a 1.5 times increase. This calculator applies that 1.5 multiplier automatically when you pick the island placement.

Make-up air is fresh outdoor air brought into the home to replace what a strong exhaust fan blows out. The International Residential Code (IRC M1503.4) and most jurisdictions that follow it require a dedicated make-up air supply once a kitchen exhaust fan is rated above 400 CFM. Without it, a powerful hood can depressurize a tight house and backdraft a gas water heater, furnace, or fireplace, pulling combustion gases indoors. This tool flags when your recommended CFM crosses that 400 CFM line so you can plan for it.

Match the duct to the airflow so it does not choke the fan: roughly 4 inch round for up to 200 CFM, 6 inch up to 400 CFM, 7 inch up to 600 CFM, 8 inch up to 900 CFM, and 10 inch or larger above that. Keep the run short and straight, use smooth-wall rigid duct instead of flexible duct, and vent to the outside rather than recirculating. An undersized or kinked duct can cut a hood's real airflow well below its rated CFM.

No, it gives a planning estimate based on standard rule-of-thumb sizing, not a full engineered ventilation design. Local building codes, make-up air requirements, duct routing, and unusually high-output or commercial-style ranges can change what you actually need. Confirm your final hood and any make-up air provisions with your local code official or a qualified HVAC professional before you buy or install.