How to Calculate CFM for Range Hoods: 5 Steps

What Is CFM for a Range Hood?

CFM stands for cubic feet per minutethe amount of air your hood can move in a minute.
In normal-person terms: it’s the hood’s “suction power,” measured as airflow. Higher CFM can capture more smoke,
grease, steam, and odorsif the hood is installed and ducted correctly.

But here’s the catch: a big CFM number on a box doesn’t guarantee big performance in your kitchen. Duct size,
duct length, elbows, roof caps, and even how high the hood sits above the cooktop can reduce real airflow.
So the goal isn’t “maximum CFM forever.” The goal is right-sized CFM that’s effective, comfortable,
and code-friendly.

Step 1: Gather Your Numbers (No Tape Measure Drama)

Before you calculate anything, collect these basics. You’ll use them to estimate your baseline CFM and then
adjust for real-world conditions.

1) Cooktop/range width

• Common sizes: 30″, 36″, 48″
• Wider cooking surfaces usually need more capture area and airflow.

2) Fuel type (gas vs. electric/induction)

• Gas creates combustion byproducts and typically needs more ventilation.
• Electric/induction still creates grease, smoke, and moisture, but often less heat plume intensity.

3) Total burner output (BTUs) if you have gas

• Look at the spec sheet or manual for total BTUs (all burners combined).
• If only individual burner BTUs are listed, add them up.

4) Kitchen volume (optional but useful)

• Kitchen volume (cubic feet) = length × width × ceiling height
• This helps as a secondary “air-exchange reality check,” especially for open layouts.

5) Hood type and venting plan

• Wall-mounted, under-cabinet, insert/liner, island, downdraft
• Ducted to outside (best for removing pollutants) vs. recirculating (filters odors/grease, not gases/moisture)

Once you have these, you’re ready to calculate a baseline. And yes: you can do this with a calculator, not a crystal ball.

Step 2: Calculate a Baseline CFM (Use Two Methods, Choose the Higher)

A practical approach is to calculate CFM using two common methods and then use the higher number as your baseline.
This keeps you from under-ventilating when one method lowballs your needs.

Method A (Gas ranges): BTU-based baseline

A widely used rule of thumb is:

Baseline CFM = Total BTUs ÷ 100

Example: If your burners total 60,000 BTU:
60,000 ÷ 100 = 600 CFM

Method B (Width-based baseline): Cooktop size

When BTUs aren’t available (common with electric/induction) or when you want a second opinion, use a width method:

• Electric/induction: ~100 CFM per linear foot of cooktop width
• Gas (especially pro-style/high output): often ends up higher via the BTU method, but width still helps as a reasonableness check

Formula:

Baseline CFM = (Cooktop width in inches ÷ 12) × 100

Example: 30″ cooktop → (30 ÷ 12) × 100 = 2.5 × 100 = 250 CFM

Quick guidance: which baseline should you trust?

• If you have a gas range, the BTU method usually leads the decision.
• If you have electric/induction, the width method is typically the starting point.
• If you cook often at high heat (searing, wok cooking, frying), pick the higher result and plan for good ducting.

Now that you have a baseline, you’ll tune it to match how hoods actually work in real kitchens.

Step 3: Adjust for Hood Style, Coverage, and Mounting Height

Your hood isn’t just a fanit’s a capture device. If it can’t “catch” the plume, the fan ends up heroically exhausting
the air behind your head while the smoke hangs out near the ceiling like it pays rent.

A) Make sure the hood is wide enough

• Minimum: hood width should be at least the cooktop width.
• Better: extend coverage by a few inches on each side when possible for improved capture.

B) Island hoods usually need more CFM

Island setups are exposed on all sides, which makes capturing the cooking plume harder. If your baseline CFM is calculated
for a wall setup, consider increasing the target for an island installation.

• Practical adjustment: add ~20–30% for island hoods if your setup is breezy/open.

C) Mounting height matters (higher = harder capture)

Most hoods have a recommended mounting range. If your hood is installed higher than the ideal, it may need more airflow
to compensate. A common manufacturer-style guideline is to bump CFM upward when installation height increases.

Practical adjustment idea:

• If you must install higher than recommended, consider adding capacity (or choosing a deeper hood) rather than hoping for the best.

D) Consider your cooking style (the “bacon factor”)

• Light cooking: simmering, boiling pasta, occasional sauté → baseline may be enough.
• Medium cooking: frequent sautéing, roasting, mild frying → baseline + a modest buffer.
• Heavy cooking: searing steaks, wok cooking, high-BTU burners, frequent frying → baseline + a stronger buffer and careful duct design.

After this step, you should have a “goal CFM” that matches your hood style and how you actually cooknot how you cook in aspirational cooking montages.

Step 4: Adjust for Ductwork (The Silent CFM Thief)

Ductwork is where good airflow goes to get humbled. Even a great blower can underperform if the duct run is long,
undersized, or shaped like a theme park ride.

A) Prefer smooth, rigid metal ducting

• Smooth, rigid ducting tends to move air more efficiently than flexible or heavily corrugated ducting.
• Fewer bends = less resistance = more real airflow.

B) Count elbows and estimate “equivalent length”

A simple way to estimate duct losses is to convert elbows into an equivalent length of straight duct.
Then you can judge whether your run is short/easy or long/complex.

• Example guideline: a 90° elbow can be treated as several feet of duct length (varies by design and source).
• Long runs can require larger duct diameter or more fan capacity to maintain performance.

C) Apply a practical performance buffer

Because homeowners rarely have fan curves and static-pressure calculations handy, here’s a practical method:

1. Easy duct run: short, straight, properly sized, minimal elbows → add ~0–10% buffer
2. Moderate duct run: a couple elbows, medium length → add ~15–25% buffer
3. Challenging duct run: long run, multiple elbows, roof cap, transitions → add ~25–40% buffer

D) Match duct size to the hood’s needs

Duct diameter matters. A powerful hood through a too-small duct is like trying to drink a milkshake through a coffee stirrer:
technically possible, emotionally upsetting, and louder than it should be.

• Many higher-CFM hoods specify larger ducts (commonly 6″, 8″, 10″ depending on airflow).
• Follow the hood manufacturer’s duct size guidance whenever possible.

After this step, you’ll have a more realistic “adjusted target CFM” that accounts for how air actually exits your home.

Step 5: Sanity-Check for Makeup Air, Noise, and Real-Life Use

Before you finalize your target CFM, run three quick checks that can save you from expensive surprises.

A) Makeup air: the 400 CFM checkpoint

Many U.S. jurisdictions that follow model residential mechanical code language require makeup air when a kitchen hood exceeds
400 CFM. In plain terms: if you exhaust a lot of air, you need a planned way for replacement air to enterso your home doesn’t
depressurize and cause backdrafting or poor hood performance.

If you’re targeting above 400 CFM, treat makeup air planning as part of the project, not an optional side quest.

B) Noise (sones) and usability

A hood that’s “powerful” but unbearably loud often gets used on lowor not used at all. Look for a hood with multiple speeds and reasonable
sound ratings at the speeds you’ll actually use day-to-day.

• Tip: If you plan to size up for heavy cooking, pick a hood that can run quietly at mid-speed and reserve high speed for smoke emergencies.

C) Ducted vs. ductless reality check

Ductless (recirculating) hoods can help with odors and grease (with the right filters), but they don’t remove moisture and combustion pollutants
the same way a ducted hood does. If you cook frequentlyespecially with gasducting to the outdoors is usually the performance winner.

After these checks, your final answer should be a CFM range you can shop with confidencewithout accidentally building a small wind tunnel in your kitchen.

Worked Examples: CFM Calculations You Can Copy-Paste Into Real Life

Example 1: 30-inch electric/induction cooktop (typical home cooking)

• Cooktop width: 30″
• Fuel: electric/induction
• Duct run: fairly short with 1–2 gentle turns
• Cooking style: mostly sautéing, boiling, occasional pan-fry

Method B (width-based): (30 ÷ 12) × 100 = 2.5 × 100 = 250 CFM baseline

Adjust for cooking style: add ~10% → 250 × 1.10 = 275 CFM

Adjust for moderate duct: add ~15% → 275 × 1.15 = 316 CFM

Shopping target: around 300–350 CFM, preferably ducted, with a quiet mid-speed you’ll actually use.

Example 2: 36-inch gas range, total 60,000 BTU (frequent cooking)

• Range: 36″
• Total BTUs: 60,000
• Hood type: wall-mounted canopy
• Duct: medium run, 2 elbows, roof cap

Method A (BTU-based): 60,000 ÷ 100 = 600 CFM baseline

Height/coverage: normal mounting, good hood width → no extra needed here

Duct complexity: add ~25% buffer → 600 × 1.25 = 750 CFM

Shopping target: 700–800 CFM with properly sized ductingand plan for makeup air considerations if required in your area.

Example 3: 48-inch gas range, total 90,000 BTU (high-heat, serious searing)

• Range: 48″
• Total BTUs: 90,000
• Hood type: island hood (harder capture)
• Duct: longer run, multiple elbows

Method A: 90,000 ÷ 100 = 900 CFM baseline

Island adjustment: add ~25% → 900 × 1.25 = 1,125 CFM

Challenging duct: add ~25% → 1,125 × 1.25 = 1,406 CFM

Shopping target: consider a system around 1,200–1,500 CFM only if you can support it with correct duct sizing,
makeup air planning, and a design that stays usable (noise control, multi-speed, potentially remote/in-line blowers).

Common Mistakes That Make a “Perfect” CFM Calculation Fail

1) Buying CFM without buying capture

A shallow hood mounted too high can miss the plume. Bigger CFM can’t fix airflow it never captures in the first place.
Prioritize good hood width, depth, and correct mounting height.

2) Undersizing the duct

A strong blower fighting a small duct can get loud, inefficient, and disappointing. Follow duct size guidance for your hood.
If you’re upsizing CFM, make sure the ducting can keep up.

3) Ignoring elbows and long runs

Every turn adds resistance. A “works on paper” CFM can become a “why does my kitchen still smell like last Tuesday?”
CFM if ductwork is long and twisty.

4) Forgetting makeup air above 400 CFM

Strong hoods can depressurize tight homes. If you plan to exceed 400 CFM, make makeup air part of your plan earlybefore the inspector (or your furnace)
complains.

5) Choosing a hood so loud you never use it

The best hood is the one you actually turn on. Look for good performance at mid-speed, reasonable sound ratings, and filters you’ll realistically clean.

Extra: Real-World Experiences & Lessons Learned ()

Ask a handful of homeowners, remodelers, or anyone who’s ever burned garlic (so… everyone), and you’ll hear the same theme:
range hood performance is less about the biggest CFM number and more about the whole system working together. One common
experience is the “I bought 600 CFM and nothing changed” moment. The culprit is often ductingespecially a long run with
multiple elbows or a duct that narrows somewhere behind the cabinets. The hood still runs, but the airflow at the cooking
surface feels underwhelming, and odors linger like they’re auditioning for a permanent role.

Another frequent real-life lesson: capture beats brute force. People who upgrade from a shallow under-cabinet
hood to a deeper canopy often report a bigger improvement than expectedeven at similar CFMbecause the deeper hood catches
the plume before it spreads. This is especially noticeable when pan-frying or searing, where the smoke rises fast and fans
out. A hood that extends a bit wider and deeper can “catch” that smoke early, making the kitchen feel cleaner even without
going to extreme airflow.

Then there’s the “why is my house whistling?” experience, which can happen when a powerful hood runs in a relatively tight home.
Doors may pull shut, the fireplace may backdraft, or the hood seems to struggle because it can’t get replacement air. That’s
where makeup air planning becomes more than a code checkboxit’s comfort and safety. Homeowners often describe the difference
as night and day once replacement air is provided properly: the hood sounds smoother, odors clear faster, and the whole system
feels less strained. In other words, the hood finally gets to do the job you paid for, instead of fighting your home like it’s
in a tug-of-war with physics.

Noise is another real-world dealbreaker. Many people discover that a “powerful” hood that’s unpleasantly loud ends up being used
only on the lowest speed. The result is a predictable cycle: cooking smells linger, grease builds up, and the homeowner concludes
the hood “doesn’t work,” when the real issue is that it’s too obnoxious to run at the speed that actually clears the air. The
better experience tends to come from choosing a hood with a comfortable mid-speed you can leave on during cooking, plus a higher
“boost” setting for smoke emergencies.

Finally, maintenance matters more than people expect. Filters that aren’t cleaned regularly reduce airflow and increase noise.
Homeowners who set a simple routinelike checking filters monthly and cleaning them on a scheduleoften report that their hood
keeps performing like new. The takeaway from all these experiences is simple: calculate a smart CFM baseline, adjust for your
hood type and ductwork, and make sure the system is usable day-to-day. The best ventilation plan isn’t the one that looks toughest
on a spec sheetit’s the one that keeps your kitchen air clean on a Tuesday night when dinner gets a little… enthusiastic.