Range hood CFM calculator
Size a range hood at about 100 CFM per foot of cooktop width on a wall and 150 CFM per foot on an island, or 1 CFM per 100 BTU for gas, whichever is higher. A 30 in wall hood over a 45,000 BTU gas range needs about 450 CFM, and above 400 CFM the IRC requires makeup air.
Updated · By the Interior Redesign AI editorial team · Sources cited on the page
Recommended hood airflow
490 CFM
Set by the gas burners (1 cfm per 100 BTU), plus 35 cfm for the duct run.
Hood width
36 in
3 in wider each side
Mount height
24-30 in
above the cooking surface; follow the hood's manual
| Width rule (100 cfm per ft) | 250 cfm |
|---|---|
| Gas rule (BTU ÷ 100) | 450 cfm |
| NKBA minimum | 150 cfm |
| Duct allowance (retailer rule of thumb) | +35 cfm |
| Recommended | 490 cfm |
- CheckOver 400 cfm: the IRC (M1503.6) requires makeup air for hoods that can exhaust more than 400 cfm. Ask your contractor and check your local code.
- OKDuct it outside. The IRC calls for at least 100 cfm, ducted outdoors, never into an attic or soffit.
Planning estimate. The hood's own installation manual and your local mechanical code decide the final size, duct diameter and height.
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Key numbers
- Wall hood (HVI)
- 100 CFM per linear foot of range
- Island hood (HVI)
- 150 CFM per linear foot of range
- Gas ranges
- About 1 CFM per 100 BTU of total burner output
- NKBA recommended minimum
- 150 CFM, ducted outdoors
- IRC minimum
- 100 CFM, ducted outdoors (M1507.4)
- Makeup air
- Required by the IRC above 400 CFM (M1503.6)
- Mounting height
- 24 in to a protected surface; 30 in to combustibles (IRC M1901.1)
Worked example
A 30 in gas range on an outside wall
Wall hood, 45,000 BTU total across the burners, 10 ft of duct with one elbow, wall cap.
- Width rule: 2.5 ft × 100 CFM = 250 CFM.
- Gas rule: 45,000 BTU ÷ 100 = 450 CFM (the larger, so it sets the base).
- Duct allowance: 10 ft × 1 + 1 elbow × 25 = 35 CFM.
- Total: 450 + 35 = 485, rounded up to 490 CFM.
- Hood width: 36 in, 3 in wider than the range on each side, common practice for gas.
Buy a hood rated about 490 CFM, 36 in wide. That is over 400 CFM, so plan makeup air with your contractor.
How we calculate
We take the largest of three published rules: the Home Ventilating Institute's 100 CFM per linear foot of range for a wall hood (150 for an island, where there is no wall to guide the smoke), 1 CFM per 100 BTU of total gas burner output (Broan-NuTone), and NKBA's 150 CFM recommended minimum.
Long ducts, elbows and roof caps add resistance, so we add a retailer rule of thumb: 1 CFM per foot of duct, 25 per elbow and 40 for a roof cap. That allowance is a heuristic, not a duct design; the hood maker's duct charts are more accurate.
If the result passes 400 CFM, we flag makeup air: the International Residential Code requires a way to bring in replacement air for hoods that can exhaust more than 400 CFM. Many cities adopt the IRC with changes, so check with your building department.
Estimates, sources
Planning estimates and published guidelines, not quotes, designs or code rulings. Local prices, your home and your jurisdiction's adopted code decide the real answer: get local bids and check with your inspector.
- Range Hood ventilation guide (Home Ventilating Institute (HVI), 2008): recommended 100 cfm per linear foot of range (wall hood), 150 cfm (island); minimum 40 / 50
- What is the required CFM to meet your needs (Broan-NuTone, 2024): gas cooktops: about 100 cfm per 10,000 BTU of total burner output; longer ducts need more cfm
- Kitchen Planning Guidelines with Access Standards (National Kitchen & Bath Association (NKBA), 2015): work triangle 26 ft max, legs 4-9 ft; aisles 42 in (one cook) / 48 in (two); walkways 36 in; seating clearance 32/36/44 in; knee space 24 in wide; landing areas; 150 cfm ventilation; storage frontage
- International Residential Code 2021, Section M1503.6 Makeup air required (International Code Council (ICC), 2021): kitchen exhaust hood systems able to exhaust more than 400 cfm need makeup air at about the same rate; hoods must discharge outdoors (M1503.1)
- Calculating your CFM (duct allowances) (Proline Range Hoods, 2024): retailer rule of thumb: add 1 cfm per foot of duct, 25 cfm per elbow, 40 cfm for a roof cap
Range hood CFM by cooktop size
For electric and induction cooktops the width rule decides. For gas, compare it with the BTU rule and use the higher number.
| Cooktop width | Wall hood | Island hood |
|---|---|---|
| 24 in | 200 CFM | 300 CFM |
| 30 in | 250 CFM | 375 CFM |
| 36 in | 300 CFM | 450 CFM |
| 48 in | 400 CFM | 600 CFM |
When do you need makeup air?
Under the IRC, a kitchen exhaust system that can move more than 400 CFM needs makeup air at roughly the same rate, with a damper that opens when the hood runs. A 36 in island hood at 450 CFM already crosses that line. Without makeup air, a big hood can starve itself of air or pull exhaust from a water heater or fireplace.
If you want to stay under 400 CFM, pick a hood with good capture (deeper canopy, wider than the cooktop) and run it on a lower speed; buy for capture, not just the CFM number.
How to use this tool
Enter the cooktop
Its width, whether the hood is on a wall or an island, and gas or electric.
Add gas output
For gas, the total BTU of all burners from the spec sheet.
Describe the duct
Duct length, number of elbows and whether it exits through the roof.
Read the size
Recommended CFM, hood width, mounting height and the makeup-air flag.
Questions
How many CFM do I need for my range hood?
About 100 CFM per foot of cooktop width for a wall hood and 150 for an island hood, or 1 CFM per 100 BTU for gas, whichever is higher, plus extra for long ducts. NKBA recommends at least 150 CFM.
How many CFM for a 30 inch range hood?
250 CFM by the width rule on a wall, 375 on an island. A gas range with 45,000 BTU total pushes it to about 450 CFM.
How many CFM for a 36 inch range hood?
300 CFM on a wall and 450 on an island by the width rule, more for high-output gas ranges.
Do I need makeup air for a range hood?
The IRC requires makeup air for kitchen exhaust hoods able to move more than 400 CFM. Local codes vary, so ask your building department before you buy a large hood.
Can a range hood be too powerful?
Yes. An oversized hood is loud, can depressurize the house and may need makeup air. Size it to the rule, then choose a hood with good capture rather than chasing CFM.
How high should a range hood be above the stove?
Usually 24 to 30 in above the cooking surface. The IRC allows 24 in to a protected surface such as an approved hood, and 30 in to unprotected combustibles; follow the hood's manual.
Should the hood be wider than the cooktop?
At least as wide. Adding 3 in on each side is common practice for island hoods and powerful gas ranges, because smoke spreads as it rises.
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