Wildfire Smoke CADR Calculator: Match Your Air Cleaner to the Room

Short Answer

If you already found the tobacco smoke CADR number on an air cleaner, you can turn it into a room-size estimate quickly.

For an 8-foot ceiling, EPA’s room-sizing checkpoint is a tobacco smoke CADR of at least two-thirds of the room’s square footage. In calculator form, that gives you two useful shortcuts:

What You Know	Use This
Room size	square footage × 0.67 = minimum tobacco smoke CADR
Smoke CADR	tobacco smoke CADR × 1.5 = largest approximate 8-foot-ceiling room

So a 120 smoke CADR purifier is roughly a 180-square-foot-room plan. A 200 smoke CADR purifier is roughly a 300-square-foot-room plan. If your living room, kitchen, and hallway share air, use the connected area, not the nicer-sounding room name.

Start With The CADR Number You Have

This worksheet is for the moment after label decoding. You have a tobacco smoke CADR number, or you have an EPA-tested DIY air-cleaner estimate, and you want to know where it can realistically go during wildfire smoke.

The common kitchen-table scene is simple: the air outside smells smoky, someone wants to put the purifier in the biggest room, and the box says a number that feels technical enough to trust. This is where I would slow down and convert the number before choosing the room.

CADR means Clean Air Delivery Rate. For wildfire smoke sizing, use tobacco smoke CADR, because EPA treats it as the small-particle category and wildfire smoke PM2.5 is a fine-particle problem.

Inverse Lookup: Smoke CADR To Largest Room

Use this table when you already know the smoke CADR and want the largest approximate room size for an 8-foot ceiling.

These are sizing checkpoints, not promises that the air will feel smoke-free.

Tobacco Smoke CADR	Largest Approximate 8-Foot-Ceiling Room
65	100 sq ft
100	150 sq ft
120	180 sq ft
150	225 sq ft
200	300 sq ft
250	375 sq ft
300	450 sq ft
335	500 sq ft
400	600 sq ft

I would round down the room, not up the promise. A purifier rated at 198 smoke CADR is close to a 300-square-foot target on paper, but smoke-day planning is not helped by pretending every real room behaves like a test chamber.

Room-To-CADR Worksheet

If you are starting from the room instead, measure the space and calculate the minimum smoke CADR.

Worksheet Line	What To Enter	How To Use It
Room length × width	Square footage	This sets the sizing target
Ceiling height	8 ft, or higher than normal	The simple EPA rule assumes an 8-foot ceiling
Minimum smoke CADR	Square footage × 0.67	Use tobacco smoke CADR, not dust or pollen CADR
Device or DIY estimate	Listed CADR or EPA-tested design value	Compare it with the room target
Room boundary	Door, hallway, open kitchen, frequent traffic	Connected air can make the effective room larger

The last line is where the math often gets too generous. A “300-square-foot living room” that stays open to a kitchen and hallway may behave more like a larger connected zone.

Filled Example: Bedroom

Say the room is a 10-by-15-foot bedroom.

Line	Entry
Room area	150 sq ft
Minimum tobacco smoke CADR	150 × 0.67 = about 100
Available purifier	Tobacco smoke CADR 120
Worksheet answer	Plausible fit

This is the kind of room where a modest portable unit can make sense, assuming the door can stay mostly closed and the rated fan speed is tolerable enough to use.

Noise matters because CADR is tied to airflow. If the device only reaches CADR 120 on a high setting no one will run overnight, the practical plan may need a smaller room, a different device, or a lower expectation.

Filled Example: Living Room

Now take a 15-by-20-foot living room.

Line	Entry
Room area	300 sq ft
Minimum tobacco smoke CADR	300 × 0.67 = about 200
Available purifier	Tobacco smoke CADR 120
Worksheet answer	Undersized

A 120 CADR device may be a reasonable bedroom plan on paper. It is not a 300-square-foot smoke-room plan by EPA’s sizing checkpoint.

The better next move is not to run the undersized unit in the larger room and mentally upgrade it. Recalculate for a smaller bedroom, office, or den first.

Filled Example: Open-Plan Area

Open-plan spaces need stricter honesty. If a living room, dining area, and kitchen share air, count the connected area you are asking the cleaner to handle.

Suppose the connected area is about 500 square feet.

Line	Entry
Connected area	500 sq ft
Minimum tobacco smoke CADR	500 × 0.67 = about 335
Available purifier	Tobacco smoke CADR 250
Worksheet answer	Short of the target

A 250 CADR purifier can sound strong compared with a small bedroom unit. In this open-plan example, it still misses the target.

This is the clearest case for the smaller-room rule: if the device cannot meet the connected-area target, close off a room people can actually use. A 250 CADR unit is much more plausible for a 300-square-foot closed room than for a 500-square-foot open zone.

The Smaller-Room Rule

Use this rule when the answer is unclear:

Choose a smaller room when the available tobacco smoke CADR is below the room target, when the room cannot stay mostly closed, or when the rated fan speed is too loud to use.

That rule keeps the worksheet from turning into wishful thinking.

A smaller, closeable room with enough clean-air delivery is usually a more defensible smoke-day plan than a larger, nicer room served by a device that misses the number.

Where DIY Fits In The Calculator

DIY box-fan filters can be entered into the worksheet, but only as specific designs. EPA’s DIY research measured several fan-filter setups in a laboratory chamber using simulated wildfire smoke from burning pine needles.

DIY Design In EPA Research	EPA Wildfire Smoke CADR
Box fan + one 1-inch MERV 13 filter	111 ± 1
Box fan + one 1-inch MERV 13 filter + cardboard shroud	156 ± 4
Box fan + one 4-inch MERV 13 filter + cardboard shroud	248 ± 15
Box fan + two 1-inch MERV 13 filters + cardboard shroud	263 ± 22
Corsi-Rosenthal Box, four 1-inch MERV 13 filters + cardboard shroud	401 ± 31

The useful takeaway is narrow: design details can change the room answer. A single-filter setup that fits a small bedroom on paper should not be treated like a Corsi-Rosenthal-style box for a larger space.

EPA also notes that dirty filters performed poorly, so filter condition belongs in the worksheet. A clogged filter is not the same entry as a fresh, tested setup.

What Not To Add To The Room Size

Some label details may matter for other decisions, but they should not make the calculated room larger.

A HEPA claim does not replace smoke CADR. For this worksheet, the sizing question is how much clean air is delivered for smoke particles in the room you plan to use.

ENERGY STAR can matter for long run times and electricity use. It does not increase the smoke CADR you enter into the calculator.

Activated carbon may be relevant for some gases or odors. It does not replace the fine-particle smoke CADR calculation.

Ozone-producing devices should be left out of the smoke-room plan. EPA advises avoiding air cleaners and filters that intentionally produce ozone, and a device that adds ozone is not a workaround for inadequate particle CADR.

What The Evidence Supports

The source base is EPA home air-cleaner guidance, EPA wildfire-smoke preparation guidance, and EPA research on DIY air cleaners.

Those sources support a practical engineering claim: for wildfire smoke particles indoors, room-size-appropriate tobacco smoke CADR is a central sizing criterion for a portable cleaner or bounded DIY setup.

They do not prove that a specific product, room, or DIY build will improve a particular person’s symptoms. EPA notes that some HEPA air-cleaner studies have found small improvements in certain cardiovascular and respiratory health measures, but effects may not be large enough for every person to feel and are not consistent across all symptoms.

So keep the claim modest. The calculator can tell you whether a device is plausibly sized for one room. It cannot turn an undersized purifier into whole-home protection, and it cannot make a personal health guarantee.

Practical Finish

Before the next smoke day, do one dry run on paper.

Find the tobacco smoke CADR, multiply it by 1.5, and compare that room-size estimate with the room or connected area where people would actually spend time. If the number misses, move the plan to a smaller, more closeable room before shopping for extra features.

That is the useful boundary of the calculator: make the room and the clean-air delivery match.