What Size Range Hood Do I Need? CFM Calculator
If you're wondering what size range hood you need, the answer is measured in CFM — cubic feet per minute of air the hood pulls off your cooktop. Enter your cooktop type, width, and (for gas) total burner BTU, and this calculator will estimate the CFM your range hood needs and pick the closest standard hood size to shop for.
Enter your numbers
Add up the BTU ratings of all burners — typically 40,000–65,000 for a 30-inch range.
Your results
How to use this calculator
Pick your cooktop type first. If you cook with gas, enter the total BTU of all burners — you'll find each burner's rating on the range's data plate or spec sheet, and most 30-inch ranges total 40,000–65,000 BTU. If you cook with electric or induction, you only need the cooktop width, since electric sizing goes by width alone.
Enter the cooktop width in inches (24, 30, 36, and 48 are the common sizes). Your results update instantly: the required CFM from the industry sizing rules, plus the standard hood size to shop for, since range hoods are sold in fixed ratings like 200, 300, 400, 600, 900, and 1,200 CFM.
As a rule of thumb, the hood itself should be at least as wide as your cooktop — a 30-inch cooktop pairs with a 30-inch (or wider) hood — and mounted at the height the manufacturer specifies.
How it works
CFM stands for cubic feet per minute: how much air the hood moves. Kitchen ventilation is sized from the heat your cooktop produces, because heat is what carries grease, smoke, and fumes up into the hood.
For gas cooktops, this calculator uses the industry rule of 100 CFM for every 10,000 BTU of total burner output: required CFM = (total BTU ÷ 10,000) × 100. A 30-inch range with 65,000 BTU of burners needs (65,000 ÷ 10,000) × 100 = 650 CFM. Gas burns hotter and produces combustion byproducts, which is why BTU — not width — drives the sizing.
For electric and induction cooktops, it uses 100 CFM for every 12 inches of cooktop width: required CFM = (width ÷ 12) × 100. A 30-inch electric cooktop needs (30 ÷ 12) × 100 = 250 CFM, which rounds up to a standard 300 CFM hood. Electric and induction produce less waste heat than gas, so width is a good enough proxy.
The recommended hood is the smallest standard size (200, 300, 400, 600, 900, or 1,200 CFM) that covers the requirement. This is kitchen ventilation CFM — it is not the same thing as bathroom exhaust fan CFM. A bathroom fan is sized from room area and ceiling height to clear moisture; a range hood is sized from cooktop heat to capture grease and fumes. The two numbers are not interchangeable, so don't apply a bathroom fan rule to a range hood.
One more thing about ducted vs. ductless: the CFM math is the same, but a ducted hood that exhausts outside will capture far more grease, heat, and smoke than a ductless (recirculating) hood that filters air and blows it back into the kitchen. If you must go ductless, choose the higher end of the range — but no amount of CFM fully makes up for not venting outside.
These are industry sizing guidelines for planning, not building code requirements. Duct length, bends, and filter type all reduce real-world airflow, and many codes require dedicated make-up air for hoods over about 400 CFM. Always check your local code and the hood's installed ratings — or ask a licensed contractor — before buying.
Frequently asked questions
How many CFM do I need for a 30-inch gas range?
Use the gas rule: 100 CFM for every 10,000 BTU of burner output. A typical 30-inch gas range with four burners totals roughly 40,000 to 65,000 BTU, so it needs about 400 to 650 CFM — for 65,000 BTU that's 650 CFM. You would buy a 900 CFM hood, the next standard size up.
What CFM range hood do I need for an electric cooktop?
Use the width rule: 100 CFM for every 12 inches of cooktop width. A 30-inch electric cooktop needs 250 CFM, which rounds up to a standard 300 CFM hood. Induction cooktops follow the same electric rule.
Is range hood CFM the same as bathroom fan CFM?
No. This calculator sizes kitchen ventilation — capturing grease, smoke, steam, and combustion heat over a cooktop — using cooktop width or burner BTU. Bathroom exhaust fans remove moisture and are sized from room area and ceiling height. The two CFM numbers are not interchangeable, so don't use a bathroom fan rule for a range hood.
Ducted or ductless — does the CFM rule change?
The CFM calculation is the same, but ducted hoods are strongly recommended: they exhaust heat, grease, and fumes outside. Ductless (recirculating) hoods push filtered air back into the kitchen and capture far less grease and heat, so choose the higher end of the range and expect a compromise. CFM alone can't fix a recirculating hood's limits.
Can a range hood be too powerful?
Mild oversizing is fine — a 900 CFM hood for a 650 CFM requirement clears smoke faster. But very powerful hoods can create negative air pressure in a tight house, and many building codes require dedicated make-up air for hoods over about 400 CFM. Check your local code before installing a high-CFM hood.