Range Hood CFM Calculator

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Starting setup:

Presets fill the whole plan; editing a setup field switches the label to Custom.

Hood location:

Location changes the width driver and capture-width check.

Vent route:

Use ducted outdoors for a ventilation target that can remove heat, moisture, and combustion products.

Cooking appliance:

Electric and induction setups do not use the BTU driver.

Hood width:

HVI width guidance is based on linear feet of hood or range.

Cooking surface width:

Island plans screen for extra hood overhang around an exposed plume.

Total burner output:

Enter the source unit printed by the range manufacturer.

Kitchen length × width:

The pair shares one unit and feeds the room-volume screening driver.

Ceiling height:

Use the average height over the kitchen zone.

Cooking intensity:

Higher heat, searing, wok cooking, and open layouts increase the room-volume driver.

Candidate hood rating:

The comparison does not predict installed airflow after duct losses.

Round-equivalent duct diameter:

Use the actual round size or round-equivalent area for a rectangular duct.

Makeup-air code screen:

Set the threshold from the adopted local rule; 400 CFM is the default screen.

Planned makeup airflow:

When the code screen is exceeded, compare planned replacement air with the full exhaust target.

Buying reserve:

Adds optional headroom to the largest airflow driver.

Straight duct run:

Enter the approximate straight run before fittings.

Duct elbows:

Count the elbows in the planned exhaust route.

count

Duct type:

Use the hood manual for permitted materials.

Minimum airflow floor:

Leave zero unless an applicable requirement supplies a minimum.

Measure	Value	Planning meaning	Copy
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The largest driver sets the base; optional reserve is applied once before rounding up to the next 25 CFM.

Check	Status	What to do	Copy
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These are model and code screens, not approval. Confirm the hood manual, adopted code, duct route, and combustion-safety conditions.

The chart shows which sizing input controls the final target.

A range hood works best when it captures the cooking plume before heat, grease, steam, odor, and combustion products spread through the kitchen. Fan capacity matters, but airflow alone cannot correct a hood that is too narrow, mounted poorly, or connected to a restrictive duct. A well-matched system combines capture area, airflow, an outdoor exhaust route, and a path for replacement air.

Cubic feet per minute, or CFM, describes airflow volume. Residential sizing guidance commonly relates CFM to hood width, while gas-appliance guidance also considers total burner output. Room size and cooking intensity add another planning view because a large open kitchen or frequent high-heat cooking can demand more air movement than width alone suggests.

Range hood planning factors and why they matter
Factor	Why it changes the plan
Hood location and width	Island plumes are exposed to cross-drafts and use stronger width guidance than wall-mounted hoods.
Cooking load	Gas output and high-heat cooking can produce a larger, faster plume.
Duct route	Small ducts, rough surfaces, long runs, and fittings increase velocity, noise, and pressure loss.
Makeup air	High exhaust rates can depressurize a home unless replacement air is available.

A ducted hood sends contaminants outdoors. A recirculating hood can filter some grease and odor, but it returns heat, moisture, and combustion products to the room. The two arrangements should not be treated as equivalent ventilation even when their fan ratings look similar.

Certified airflow is still a laboratory rating, not a promise of installed performance. Actual delivery depends on the hood, mounting height, duct diameter, route, fittings, termination, and pressure conditions in the home. Manufacturer instructions and adopted local code remain the final authority, especially for professional-style appliances, downdrafts, and homes with naturally drafted fuel-burning equipment.

How to Use This Tool:

Start with the appliance and physical installation, then compare the result with a real hood rating.

Choose the hood location, vent route, and cooking appliance. A preset can provide a complete example, but replace its values with the actual kitchen and appliance specifications.
Enter hood and cooking-surface widths, total burner output when gas is selected, and the kitchen dimensions. Keep the displayed units attached to each measurement.
Set cooking intensity, the candidate hood rating, duct diameter, makeup-air threshold, and any planned replacement airflow. Use the adopted local threshold rather than assuming the default applies everywhere.
Review the rounded hood target first, then resolve any candidate, capture-width, duct, makeup-air, or vent-route warning before selecting equipment.

Interpreting Results:

The largest airflow driver sets the base target. A candidate marked Short is more than 10% below that rounded target; Borderline is below it by up to 10%; and Sized is from the target through 35% headroom. More than 35% headroom is flagged because extra capacity may bring more noise, larger ductwork, and additional makeup-air work.

Capture width checks geometry, not fan strength. A narrow hood can miss an exposed plume even when its CFM rating is high.
Duct route is a screening result. Confirm the permitted diameter, material, length, elbows, and termination in the hood manual.
Makeup air changes to review required only when the rounded target strictly exceeds the configured threshold. A value exactly equal to the threshold remains below this screen.
Vent route identifies whether cooking air is exhausted outdoors. A recirculating result is not an outdoor-ventilation plan.

Technical Details:

The airflow target is the greatest of four independent planning drivers: width guidance, gas burner output, a room-volume air-change screen, and any entered minimum. An optional reserve is applied once to that controlling value, then the result is rounded upward to a 25 CFM step.

Formula Core

For a wall hood, width guidance uses 100 CFM per linear foot. Island and downdraft selections use 150 CFM per linear foot. The burner-output driver applies only to gas selections.

\begin{aligned} Q_{width} & = \frac{W}{12} \times R \\ Q_{gas} & = \frac{B}{100} \\ Q_{room} & = \frac{L \times D \times H \times A}{60} \end{aligned}

Here, W is hood width in inches, R is 100 or 150 CFM per foot, B is total burner output in BTU/h, L × D × H is kitchen volume in cubic feet, and A is the selected 10, 15, 20, or 25 air changes per hour. The air-change values are planning assumptions rather than code requirements.

Q_{target} = 25 \times ⌈ \frac{\max (Q_{width}, Q_{gas}, Q_{room}, Q_{minimum}) \times (1 + \frac{p}{100})}{25} ⌉

With a 42-inch wall hood, 60,000 BTU/h gas range, 14 × 14 × 9 foot kitchen, 20 ACH setting, and no reserve, the drivers are 350, 600, and 588 CFM. The 600 CFM burner driver controls, and 25 CFM rounding leaves the target at 600 CFM.

Rule Core

Range hood screening rules and exact boundaries
Check	Rule	Meaning
Candidate headroom	(candidate − target) ÷ target × 100	Short below −10%; Borderline from −10% to below 0%; Sized from 0% through 35%; Large headroom above 35%.
Makeup-air screen	Target > configured threshold	The equality case does not trigger the screen. When triggered, planned makeup air is compared with the full target.
Duct velocity	CFM ÷ round duct area	The suggested diameter is the first available size whose target velocity is at most 1,800 ft/min. A selected route above 2,200 ft/min is warned if the diameter is not already flagged small.
Equivalent route	(straight feet + 5 × elbows) × duct multiplier	Multipliers are 1.00 for smooth, 1.12 for semi-rigid or mixed, and 1.28 for flexible or rough duct. More than 45 feet is flagged after diameter and velocity checks.
Capture width	hood width − cooktop width ≥ required overhang	The island screen requires at least 6 inches total extra width; wall and downdraft screens require no added width.

Airflow conversions use 1 CFM = 1.69901082 m³/h and 1 CFM = 0.47194745 L/s. Input units are converted before calculation, full precision is retained internally, and only the final target is forced upward to the next 25 CFM.

Accuracy and Safety Notes:

This is a planning estimate, not an equipment approval or mechanical design. It does not calculate pressure loss from an actual fitting schedule, predict capture efficiency, verify certified ratings, or assess combustion depressurization.

Use the cooking-appliance and hood manufacturers' ventilation tables when they specify a higher airflow, different capture geometry, or particular duct size.
Confirm the adopted code and local amendments. The 400 CFM default is only a screen, and the 2024 IRC condition depends on the fuel-burning appliances and venting arrangement inside the dwelling.
Have makeup air and combustion safety reviewed by a qualified professional when high exhaust, a tight building envelope, or naturally drafted appliances can interact.

References:

How Much Ventilation Do I Need?, Home Ventilating Institute.
2024 International Residential Code, Chapter 15 Exhaust Systems, International Code Council, 2024.