Enter your cooktop: its width, gas or electric, against a wall or on an island. You get the hood’s width, the fan power (CFM) it needs, the duct, and whether the code asks for make-up air.
Range hood
36″ hood, at least 400 CFM30″ at the least · a 6″ round duct · no make-up air at 400 CFM
Quick answer: a range hood should be at least as wide as the cooktop, better 3″ wider each side: a 30″ cooktop takes a 30–36″ hood, and on an island 36–42″. For its fan, the Home Ventilating Institute recommends 100 CFM per foot of cooktop against a wall and 150 on an island; a gas cooktop wants its total BTUs ÷ 100 if that is more. Past 400 CFM, check whether the code wants make-up air.
How to use the range hood calculator
- Pick gas or electric (induction counts as electric), and whether the cooktop is against a wall or on an island.
- Enter the cooktop’s width: 30″ and 36″ are the usual ones.
- For gas, add up the burners’ BTUs. The spec sheet lists each burner (hood maker Hauslane’s worked example totals 40,000 BTU).
- Say whether a gas water heater, furnace or fireplace vents on its own inside. It decides whether a strong hood needs make-up air. Copy link keeps the result.
The rules behind the numbers
Airflow: 100 CFM a foot, 150 on an island
The Home Ventilating Institute (HVI), which certifies fan ratings, recommends 100 CFM for each linear foot of cooktop against a wall, and at least 40. On an island, where nothing beside the cooktop holds the smoke in, “multiply the rate by 1.5”: 150 CFM a foot, 50 at least. A 30″ (2½ ft) cooktop gets 250 CFM against a wall.
Gas: the burners’ BTUs ÷ 100
Gas burners put out more heat and fumes. Hood maker Hauslane’s rule: add up the burners’ BTUs and divide by 100, so 40,000 BTU wants 400 CFM. The calculator takes whichever of the two rules asks for more. For a professional-style range, the HVI says to follow the range maker’s advice.
Width: the cooktop’s, and more
The Range Hood Store’s sizing guide: a wall hood “at least as wide as the cooking surface”, better 3″ past each side; an island hood wider still, a 36–42″ hood for a 30″ cooktop and 42–48″ for a 36″ one. Hoods are sold 24, 30, 36, 42, 48, 54 and 60″ wide. How HIGH to hang it is the kitchen cabinet height calculator‘s job.
The duct: 6″ to 400 CFM
The same guide: up to 400 CFM a 6″ round duct at least, 600–900 CFM an 8″, 1,200 and up a 10″. Where it leaves a gap, the calculator takes the next size up. The code wants the duct in galvanized steel, stainless steel or copper (IRC M1503.4).
Make-up air past 400 CFM
A strong hood pulls air out of the house, and that air comes back from somewhere, even down a water heater’s flue. The 2024 International Residential Code (M1503.6) wants make-up air, brought in at about the rate the hood exhausts, for a hood over 400 CFM where a fuel-burning appliance that vents on its own sits inside. The 2015 and 2018 editions asked it of every hood over 400, and many places still build to them. The code’s least for a kitchen is 100 CFM (Table M1505.5).
Range hood CFM by cooktop width
| Cooktop | Against a wall | On an island |
|---|---|---|
| 24″ (2 ft) | 200 CFM | 300 CFM |
| 30″ (2½ ft) | 250 CFM | 375 CFM |
| 36″ (3 ft) | 300 CFM | 450 CFM |
| 48″ (4 ft) | 400 CFM | 600 CFM |
The HVI’s recommended rates. For gas, compare with the BTU chart below and take the larger.
Gas cooktops: CFM and duct by BTU
| All burners together | CFM | Round duct |
|---|---|---|
| 30,000 BTU | 300 CFM | 6″ |
| 40,000 BTU | 400 CFM | 6″ |
| 60,000 BTU | 600 CFM | 8″ |
| 75,000 BTU | 750 CFM | 8″ |
| 100,000 BTU | 1,000 CFM | 10″ |
Range hood width by cooktop
| Cooktop | Wall hood | Island hood |
|---|---|---|
| 24″ | 24–30″ | 30–36″ |
| 30″ | 30–36″ | 36–42″ |
| 36″ | 36–42″ | 42–48″ |
| 48″ | 48–54″ | 54–60″ |
Three worked examples
A 30″ gas range against a wall, 40,000 BTU. The HVI asks 250 CFM, the gas rule 400: buy a 36″ hood of at least 400 CFM (30″ at the least) on a 6″ duct. At exactly 400 CFM, no make-up air.
A 36″ pro-style gas range, 75,000 BTU, with a gas water heater inside. The gas rule asks 750 CFM, so a 42″ hood on an 8″ duct, and the code wants make-up air: the hood is over 400 CFM and the water heater vents on its own.
A 36″ induction cooktop on an island. 3 ft × 150 = 450 CFM, under a 48″ island hood (42″ at the least) on an 8″ duct. Past 400, ask your building department about make-up air.
Common range hood mistakes
- A hood narrower than the cooktop. Smoke from the outer burners rises past its edges. Go at least as wide, better 6″ wider.
- A wall hood’s CFM on an island. Open on all sides, an island needs 1.5 times the airflow.
- A small duct on a big fan. The 6″ duct stops at 400 CFM in the Range Hood Store’s chart; a 600 CFM hood wants 8″. Size the duct with the fan.
- Ignoring make-up air. Past 400 CFM, a hood can pull fumes back down a water heater’s or furnace’s flue.
Planning the whole wall? Set the uppers, the counter and the hood’s height with the free kitchen cabinet height calculator, lay out the kitchen in the kitchen layout planner, and draw it to scale in the free 2D room planner.
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Range hood size and CFM questions
How many CFM do I need for my range hood?
100 CFM for each foot of cooktop against a wall, 150 on an island (the HVI). For gas, also add up the burners’ BTUs and divide by 100, and take whichever is more. A 30″ gas range of 40,000 BTU wants 400 CFM.
What size range hood do I need?
At least as wide as the cooktop, better 3″ wider on each side: 30–36″ for a 30″ cooktop, 36–42″ for a 36″ one. Over an island, 6–12″ wider than the cooktop.
How wide should a range hood be?
Never narrower than the cooktop. Hoods are sold 24, 30, 36, 42, 48, 54 and 60″ wide, so a 30″ cooktop takes a 30″ hood at the least and a 36″ one to catch more.
When do you need a 600 CFM range hood?
For a gas cooktop of about 60,000 BTU, or a 48″ cooktop on an island (4 ft × 150). Past 400 CFM, check the make-up air rule, and run an 8″ duct.
Does a range hood over 400 CFM need make-up air?
Under the 2024 International Residential Code, when a gas, oil or wood appliance that vents on its own (a water heater, furnace or fireplace) is inside the house. Earlier editions required it for every hood over 400 CFM, and many towns still use them: ask your building department.
What cooktop does a 36-inch range hood fit?
A 30″ cooktop, with 3″ to spare each side, or a 36″ cooktop exactly. Over an island, a 36″ hood suits a 24–30″ cooktop.