Kitchen Exhaust Hood CFM Sizing Calculator
Size a range hood the right way — from gas cooktop BTU output or electric cooktop width — with air-change checks, duct and make-up-air guidance, and a professional PDF report.
Gas is sized by total BTU; electric and induction are sized by cooktop width.
Add up every burner's max BTU. A typical 4-burner gas cooktop totals 40,000–50,000 BTU; pro ranges reach 90,000+.
Islands lose air on all sides, so they need more airflow per foot of cooktop.
Above 8 ft the hood mounts higher, so a margin is added for capture.
Longer ducts and elbows add resistance, so buy a blower with headroom.
The air-change rule sizes airflow to the whole room: floor area × ceiling height × air changes ÷ 60. Leave area blank to skip it.
| CFM range | Hood class | Best for | Duct size | Make-up air |
|---|---|---|---|---|
| Up to 300 | Light-duty | Small or occasional electric cooktops | 6 in | Not required |
| 300–400 | Standard | 30 in ranges, everyday cooking | 6 in | Not required |
| 400–600 | High-output | Gas up to ~60k BTU, frequent cooking | 7–8 in | Usually required |
| 600–900 | Professional | 36–48 in high-BTU, wok or grill | 8–10 in | Required |
| 900+ | Commercial-style | Pro ranges, islands, heavy searing | 10–12 in | Required |
The highlighted row is your recommended tier. Sizing rules are industry rules of thumb; hood width should be at least as wide as the cooktop, ideally 3 in past each side.
How to use the range hood CFM calculator
Enter your cooktop, tell it where the hood mounts, and the calculator runs all three industry sizing rules at once — then adds the ceiling and duct margins and rounds to a blower size you can actually buy.
Pick gas or electric
Gas is sized on total burner BTU. Electric and induction are sized on cooktop width and room volume.
Set width and BTU
Measure the cooktop, not the hood. On gas, add up every burner’s maximum rating.
Add mounting and duct
Wall or island, ceiling height, and how long the duct run is — each one changes the number.
Read the result & save a PDF
Recommended CFM, hood width, duct size, make-up air, and the tier your hood lands in.
How range hood CFM is calculated
There is no single formula — there are three, and the correct answer is whichever gives the biggest figure. One sizes to the cooktop’s footprint, one to the heat it puts out, and one to the volume of the room. The calculator runs all three, takes the largest, then adds margin for ceiling height and duct resistance.
Worked example — a 36 in gas range, 60,000 BTU, 9 ft ceiling
Width rule: 36 ÷ 12 × 100 = 300 CFM
BTU rule: 60,000 ÷ 100 = 600 CFM
Air changes, 200 sq ft room: 200 × 9 × 15 ÷ 60 = 450 CFM
Base requirement — largest of the three: 600 CFM (BTU rule governs)
Ceiling margin at 9 ft: 600 × 1.10 = 660 CFM
Typical duct run: 660 × 1.15 = 759 CFM
≈ 800 CFM recommended — a 36 in hood on 8–10 in duct, make-up air required.
Range hood CFM sizing charts
The lookups that settle most kitchen specs — CFM by cooktop width, by burner BTU, by room size, plus the duct, hood width, and make-up air figures that follow from the result.
| Cooktop width | Linear feet | Wall hood | Island hood |
|---|---|---|---|
| 24 in | 2.0 ft | 200 CFM | 300 CFM |
| 30 in | 2.5 ft | 250 CFM | 375 CFM |
| 36 in | 3.0 ft | 300 CFM | 450 CFM |
| 42 in | 3.5 ft | 350 CFM | 525 CFM |
| 48 in | 4.0 ft | 400 CFM | 600 CFM |
| 60 in | 5.0 ft | 500 CFM | 750 CFM |
Base figures before ceiling and duct margins. Measure the cooktop, not the cabinet opening — and on gas, check the BTU rule too, because it usually comes out higher.
| Total cooktop BTU | Base CFM | Typical appliance |
|---|---|---|
| 30,000 BTU | 300 CFM | Compact or 4-burner 24 in gas cooktop |
| 40,000 BTU | 400 CFM | Standard 30 in gas range |
| 50,000 BTU | 500 CFM | 30–36 in with a high-output burner |
| 60,000 BTU | 600 CFM | 36 in gas range or 5-burner cooktop |
| 75,000 BTU | 750 CFM | 48 in range or wok burner setup |
| 90,000 BTU | 900 CFM | Professional 48 in dual-fuel range |
| 120,000 BTU | 1,200 CFM | Commercial-style range with griddle |
Add every burner’s maximum rating together, including the oven burner if the range vents through the hood. Electric and induction cooktops have no BTU figure — they size on width and room volume instead.
| Kitchen floor area | 8 ft ceiling | 9 ft ceiling | 10 ft ceiling |
|---|---|---|---|
| 100 sq ft | 200 CFM | 225 CFM | 250 CFM |
| 150 sq ft | 300 CFM | 338 CFM | 375 CFM |
| 200 sq ft | 400 CFM | 450 CFM | 500 CFM |
| 250 sq ft | 500 CFM | 563 CFM | 625 CFM |
| 300 sq ft | 600 CFM | 675 CFM | 750 CFM |
| 400 sq ft | 800 CFM | 900 CFM | 1,000 CFM |
This rule catches large open-plan kitchens where a modest cooktop still sits in a big volume of air. In a tight galley it rarely governs; in a 400 sq ft great room it almost always does.
| CFM range | Hood class | Best for | Duct size | Make-up air |
|---|---|---|---|---|
| Up to 300 | Light-duty | Small or occasional electric cooktops | 6 in round | Not required |
| 300–400 | Standard | 30 in ranges, everyday cooking | 6 in round | Not required |
| 400–600 | High-output | Gas to ~60k BTU, frequent cooking | 7–8 in round | Usually required |
| 600–900 | Professional | 36–48 in high-BTU, wok or grill | 8–10 in round | Required |
| 900+ | Commercial-style | Pro ranges, islands, heavy searing | 10–12 in round | Required |
Duct sizes are working minimums for round rigid duct — always follow the manufacturer’s spec, which often calls for one size larger. Rectangular duct is sized on equivalent area, and flexible duct should be treated as a size smaller than its diameter suggests.
| Cooktop width | Minimum hood | Ideal hood | Overhang each side |
|---|---|---|---|
| 24 in | 24 in | 30 in | 3 in |
| 30 in | 30 in | 36 in | 3 in |
| 36 in | 36 in | 42 in | 3 in |
| 42 in | 42 in | 48 in | 3 in |
| 48 in | 48 in | 54 in | 3 in |
| 60 in | 60 in | 66 in | 3 in |
Hoods come in fixed sizes — 24, 30, 36, 42, 48, 54, and 60 inches. A hood narrower than the cooktop leaks smoke past the edges no matter how much CFM the blower is rated for.
Identical cooktop, identical BTU — but the island hood needs 50 percent more airflow. Mounting position decides how much of the plume ever reaches the filters.
- Walls and cabinets do free work — they hold the rising plume in place. An island has nothing on any side, so cross-draughts from doorways and HVAC vents steal smoke before the hood can pull it in.
- Mounting height compounds it — wall hoods sit 24 to 30 in above the cooktop, islands 30 to 36 in for head clearance. Every extra inch widens the plume the hood has to cover.
- Downdraft is a different animal — it fights the rising plume rather than following it, so it isn’t covered by these rules. Plan on 400 to 600 CFM and treat it as a compromise where an overhead hood won’t fit.
Everything the calculator works out
One set of cooktop details produces a full hood spec — the airflow figure, which rule drove it, and every downstream decision that follows from the number.
The figures behind every hood spec
Built for anyone specifying a range hood
Hoods are sold on CFM, but kitchens are described in inches and BTU — which is why this conversion sits between almost every hood decision and the purchase.
Upgrading a range or replacing a tired microwave-hood combo, and trying to work out whether the 400 CFM model on the shelf is enough for the cooktop they actually have.
- Add every burner’s BTU, not the biggest
- Check the 400 CFM make-up air line
- Buy the hood at least as wide as the cooktop
Pinning the ventilation spec early, because the duct route, soffit depth, and make-up air path all have to be settled before cabinetry is ordered.
- Run the island number before moving the cooktop
- Size the chase for the duct, not the reverse
- Save the PDF into the spec package
Confirming that the hood a client already bought matches the duct that’s in the wall — and flagging the make-up air requirement before inspection does.
- Add duct margin for elbows and length
- Match duct diameter to the blower rating
- Check local code on make-up air
7 tips for getting hood sizing right
The details that separate a hood that clears a seared steak from one that just makes noise while the smoke alarm goes off.
Range hood CFM FAQ
The sizing, ducting, and code questions people ask most when they’re choosing a kitchen exhaust hood.
Take the largest of three figures: 100 CFM per foot of cooktop for a wall hood (150 per foot for an island), total gas BTU divided by 100, and the room air-change target of floor area × ceiling height × 15 ÷ 60.
A 30 inch electric cooktop against a wall lands around 250 CFM. A 36 inch gas range at 60,000 BTU needs about 600 CFM before margins. Add roughly 10 percent per foot of ceiling above 8 feet and 15 to 30 percent for a longer duct run, then round up to the next 50.
Divide the total BTU of every burner by 100. A cooktop rated at 60,000 BTU needs about 600 CFM on the BTU rule.
Use the combined maximum output of all burners, not the largest one. A typical four burner gas cooktop totals 40,000 to 50,000 BTU, while a professional range can reach 90,000 BTU or more. The BTU rule only applies to gas — electric and induction cooktops are sized on width and room volume.
Yes. Island hoods are sized at 150 CFM per foot of cooktop instead of 100, so a 36 inch island cooktop starts at 450 CFM rather than 300.
A wall hood has a back wall and usually cabinets on either side helping to funnel smoke upward. An island hood is open on all four sides, so cross-draughts from doors, HVAC vents, and foot traffic pull the plume away before it reaches the filters. Island hoods also mount higher, which widens the capture area they have to cover.
It covers a gas cooktop up to about 40,000 BTU, which is a standard 30 inch four burner model. Above that the BTU rule outruns it — a 60,000 BTU range needs around 600 CFM.
400 CFM is also the line where make-up air enters the picture. Many jurisdictions following the International Residential Code require a dedicated make-up air supply for hoods rated above 400 CFM, so staying at or under that figure can meaningfully simplify the install.
As a working minimum: 6 inch round up to 400 CFM, 7 to 8 inch from 400 to 600, 8 to 10 inch from 600 to 900, and 10 to 12 inch above 900 CFM.
Always follow the manufacturer’s specified duct size — undersizing it throttles the blower and makes the hood far louder without moving more air. Use rigid smooth-wall duct, keep elbows to a minimum, and never reduce the diameter partway along the run.
Generally once the hood is rated above 400 CFM, though the exact threshold and the exemptions vary by jurisdiction and by how tight the house is.
A powerful hood removes air faster than a sealed house can replace it, and the resulting negative pressure can backdraft a furnace, water heater, or fireplace — pulling combustion gases into the room. A make-up air system, usually an interlocked damper and sometimes a tempered supply, replaces that air deliberately. Budget for it before you buy the hood, not after.
Yes. Oversized hoods pull conditioned air straight out of the house, run louder, cost more to install because of larger ducting and make-up air, and can create backdraft risk in a tight home.
Most hoods have multiple speeds, so a higher rating is not wasted outright — but a 1,200 CFM blower over a 40,000 BTU cooktop is paying for capacity you will never switch on. Size to your actual cooking, then add margin for duct run and ceiling height rather than buying the biggest number on the shelf.
It should never be narrower. Matching the cooktop width is the minimum, and 3 inches of overhang on each side — so 6 inches wider overall — captures noticeably more of the plume.
Overhang matters most on islands and on gas, where the plume spreads as it rises. If cabinet layout will not allow a wider hood, keep the mounting height at the low end of the manufacturer’s range instead: typically 24 to 30 inches above the cooktop for a wall hood, and 30 to 36 inches for an island.
Planning Estimate Only — Not an Engineering or Code Specification: This calculator applies common industry rules of thumb for residential kitchen ventilation and does not constitute a mechanical design. Actual airflow depends on duct diameter, length, material, elbow count, termination cap, filter type, and installed static pressure, and delivered CFM is normally well below a hood’s rated figure. Make-up air requirements, permitted duct routing, termination clearances, and combustion appliance safety provisions are set by your local building and mechanical codes and by the appliance manufacturer’s installation instructions, which take precedence over any figure shown here. Ductless and recirculating hoods, downdraft systems, and commercial equipment are outside the scope of these rules. Hoods installed over solid-fuel or high-temperature appliances have separate requirements. Have ventilation, gas, and make-up air work verified by a licensed HVAC or mechanical contractor before purchase or installation.