How to Calculate Air Purifier CADR and Room Coverage for PM2.5 Malaysia

How to Calculate Air Purifier CADR and Room Coverage for PM2.5 Malaysia

Choosing an air purifier for haze and PM2.5 in Malaysia requires more than checking the advertised room coverage on a product listing.

An air purifier advertised for a large room may not provide sufficient particulate cleaning at the fan speed used in everyday operation.

Similarly, a compact purifier with an effective HEPA filter may still be undersized for a classroom, office or large living room.

One of the most useful specifications to understand is Clean Air Delivery Rate (CADR).

By combining CADR, room volume and equivalent air changes per hour (eACH), homeowners, office managers and schools can make more informed air purifier purchasing decisions.

This guide explains how to calculate air purifier CADR requirements, estimate room coverage, compare multiple purifiers and observe indoor PM2.5 changes using a portable air quality monitor such as the Temtop S1 Up.

MTM Precision Sdn Bhd supplies portable air quality monitoring instruments for homes, offices, schools and commercial applications throughout Malaysia.

1. What Is Air Purifier CADR?

Clean Air Delivery Rate (CADR) describes the rate at which an air cleaner delivers air cleaned of a specified pollutant under a defined test method.

For particulate air cleaning, CADR is commonly expressed in:

Cubic metres per hour (m³/h)

For example:

CADR 100 m³/h

CADR 200 m³/h

CADR 300 m³/h

CADR 400 m³/h

CADR 500 m³/h

A higher verified particle CADR generally indicates greater particulate cleaning capacity under the specified testing conditions.

However, CADR alone does not guarantee a particular indoor PM2.5 concentration.

Actual performance depends on:

Room size

Ceiling height

Airflow distribution

Purifier operating speed

Filter condition

Outdoor haze infiltration

Indoor particle sources

Existing ventilation and filtration

For haze-related PM2.5 removal, compare verified particle CADR rather than relying only on advertised room coverage.

2. Why Is CADR Important During Haze in Malaysia?

During haze episodes, fine airborne particles may enter homes, offices and classrooms through windows, doors, ventilation systems and building leakage.

These particles can increase indoor PM2.5 concentrations.

A suitable air purifier helps remove airborne particles by passing room air through effective filtration.

However, the purifier must deliver enough cleaned air relative to the room volume and pollution conditions.

For example, a small desktop purifier may be suitable for limited local applications but insufficient for a large shared office.

The relationship between CADR and room volume helps explain why the same purifier may perform differently in different rooms.

3. What Is PM2.5?

PM2.5 refers to airborne particles with an aerodynamic diameter of 2.5 micrometres or smaller.

Common sources include:

Forest and peatland fires

Open burning

Vehicle exhaust

Industrial combustion

Cigarette smoke

Cooking emissions

Other combustion sources

PM2.5 concentrations are generally expressed in micrograms per cubic metre (µg/m³).

Fine particles can penetrate deeply into the respiratory system.

Exposure to elevated PM2.5 is associated with adverse respiratory and cardiovascular health effects.

An appropriately selected air purifier can help reduce airborne particulate concentrations.

CADR indicates particulate cleaning capacity, while a PM2.5 monitor helps observe actual particulate conditions at a measurement location.

4. The Three Main Values Needed for CADR Calculation

To estimate the required particle CADR, users need three values.

1. Room Length

Measured in metres.

2. Room Width

Measured in metres.

3. Ceiling Height

Measured in metres.

These dimensions determine room volume.

Users must also select an appropriate equivalent clean-air change target based on the intended application and relevant technical guidance.

The basic relationship is:

Required Particle CADR = Room Volume × Target eACH

Where:

CADR is expressed in m³/h

Room volume is expressed in m³

eACH is expressed per hour

This simplified formula is useful for preliminary air purifier sizing.

It does not replace a complete ventilation or indoor air quality assessment.

5. Step 1 - Calculate Room Floor Area

The first step is to calculate floor area.

Floor Area = Length × Width

For example:

Room length = 5 metres

Room width = 4 metres

Floor area:

5 × 4 = 20 m²

This is a 20-square-metre room.

However, floor area alone does not account for ceiling height.

A room with a high ceiling contains more air than a room with the same floor area and a lower ceiling.

For CADR calculations, room volume is generally more useful than floor area alone.

6. Step 2 - Calculate Room Volume

The basic formula is:

Room Volume = Length × Width × Ceiling Height

For example:

Length: 5 metres

Width: 4 metres

Ceiling height: 3 metres

Room volume:

5 × 4 × 3 = 60 m³

This means the room contains approximately 60 cubic metres of air based on its geometric dimensions.

For irregular rooms, connected spaces or open-plan layouts, additional considerations may be necessary.

Always include ceiling height when calculating air purifier capacity.

7. Step 3 - Understand Equivalent Air Changes per Hour

Equivalent Air Changes per Hour (eACH) describes a clean-air delivery rate relative to room volume.

For a portable recirculating air purifier, a simplified calculation is:

eACH = Particle CADR / Room Volume

For example:

Particle CADR = 300 m³/h

Room volume = 60 m³

eACH = 300 / 60 = 5 per hour

This means the purifier provides nominal particle clean-air delivery equivalent to five times the room volume per hour under the stated assumptions.

It does not mean the purifier introduces five room volumes of fresh outdoor air.

A recirculating air purifier primarily filters indoor air.

Equivalent clean-air changes and outdoor ventilation air changes are not the same thing.

8. Step 4 - Calculate the Required Particle CADR

The formula is:

Required Particle CADR = Room Volume × Target eACH

Consider a hypothetical room with a volume of 60 m³.

If the selected target is five equivalent clean-air changes per hour:

60 × 5 = 300 m³/h

The illustrative required particle CADR is therefore 300 m³/h.

If the selected target is six equivalent clean-air changes per hour:

60 × 6 = 360 m³/h

The appropriate target depends on the environment, existing clean-air provision and applicable guidance.

Five or six equivalent clean-air changes per hour are calculation examples, not universal legal requirements or guaranteed safe exposure levels.

9. Interactive CADR and Room Coverage Calculator

Use the calculator below to estimate the particle CADR corresponding to your selected room dimensions and equivalent clean-air change target.

The result is intended for preliminary sizing and assumes a rectangular room and rated particle CADR at the intended fan setting.

{@body const [length,setLength] = DIL.useState("5")} {@body const [width,setWidth] = DIL.useState("4")} {@body const [ceiling,setCeiling] = DIL.useState("3")} {@body const [target,setTarget] = DIL.useState(5)} {@body const roomVolume = Number(length)*Number(width)Number(ceiling)} {@body const validRoom = Number.isFinite(roomVolume) && roomVolume>0 && Number(length)>0 && Number(width)>0 && Number(ceiling)>0} {@body const requiredCadr = validRoom ? roomVolumetarget : 0}

Air Purifier CADR Calculator Length (m) Width (m) Height (m) Target equivalent clean-air changes per hour setTarget(Number(v))} options={[{"label":"3 eACH","value":"3"},{"label":"5 eACH","value":"5"},{"label":"6 eACH","value":"6"}]}/> {#if validRoom} Room volume {roomVolume.toFixed(1)} m³ Required particle CADR {requiredCadr.toFixed(0)} m³/h GenUI.copy(`Room: ${length} m x ${width} m x ${ceiling} m\nRoom volume: ${roomVolume.toFixed(1)} m3\nTarget eACH: ${target}\nIllustrative required particle CADR: ${requiredCadr.toFixed(0)} m3/h`)}> Copy Calculation {:else} Enter positive room dimensions to calculate CADR. {/if} This calculator provides a simplified clean-air delivery estimate. It does not account for all building conditions, existing filtration, pollutant generation or ventilation requirements.

10. Example CADR Calculation for a Bedroom

Consider a bedroom in Kuala Lumpur.

Room dimensions:

Length: 4 metres

Width: 3 metres

Ceiling height: 2.8 metres

Room volume:

4 × 3 × 2.8 = 33.6 m³

At an illustrative target of five eACH:

33.6 × 5 = 168 m³/h

At six eACH:

33.6 × 6 = 201.6 m³/h

A customer may compare purifiers with verified particle CADR specifications around these values or higher.

However, the actual choice should also consider noise, fan speed, filtration and other room conditions.

A purifier's CADR at maximum fan speed may differ from its performance at a quieter night setting.

11. Example CADR Calculation for a Living Room

Consider a living room measuring:

Length: 6 metres

Width: 5 metres

Ceiling height: 3 metres

Room volume:

6 × 5 × 3 = 90 m³

At five eACH:

90 × 5 = 450 m³/h

At six eACH:

90 × 6 = 540 m³/h

This example illustrates why larger living rooms may require substantially more clean-air delivery than small bedrooms.

If the living room connects directly to a kitchen, dining area or hallway, the effective air volume may be larger.

Open-plan layouts should be assessed using the connected space rather than only the area beside the purifier.

12. Example CADR Calculation for a Six-Person Office

Consider a shared office with six employees.

Room dimensions:

Length: 7 metres

Width: 5 metres

Ceiling height: 3 metres

Room volume:

7 × 5 × 3 = 105 m³

At five eACH:

105 × 5 = 525 m³/h

At six eACH:

105 × 6 = 630 m³/h

These values illustrate a possible particulate clean-air delivery target.

The office's existing HVAC filtration and ventilation should also be considered.

If the office contains cigarette smoke, eliminating indoor smoking is essential.

An air purifier cannot eliminate all harmful smoke gases or make secondhand smoke exposure safe.

Office air purifier sizing should consider room volume, occupancy, ventilation, particulate sources and verified CADR.

13. Example CADR Calculation for a Classroom

Consider a classroom measuring:

Length: 8 metres

Width: 7 metres

Ceiling height: 3 metres

Room volume:

8 × 7 × 3 = 168 m³

At five eACH:

168 × 5 = 840 m³/h

At six eACH:

168 × 6 = 1,008 m³/h

These are illustrative total clean-air delivery values, not a requirement that all clean air must come from portable purifiers.

Existing filtered ventilation may contribute to total clean-air delivery.

Schools should follow applicable building, health and education guidance.

Portable air purifiers should complement, not replace, necessary classroom ventilation.

14. CADR Reference Table for Common Room Sizes

The following table uses a ceiling height of 3 metres.

It shows illustrative particle CADR requirements for three selected equivalent clean-air change targets.

Floor areaRoom volume3 eACH5 eACH6 eACH10 m²30 m³90 m³/h150 m³/h180 m³/h15 m²45 m³135 m³/h225 m³/h270 m³/h20 m²60 m³180 m³/h300 m³/h360 m³/h25 m²75 m³225 m³/h375 m³/h450 m³/h30 m²90 m³270 m³/h450 m³/h540 m³/h40 m²120 m³360 m³/h600 m³/h720 m³/h50 m²150 m³450 m³/h750 m³/h900 m³/h60 m²180 m³540 m³/h900 m³/h1,080 m³/h

This table is for preliminary comparison only.

Actual purifier selection should consider existing clean-air provision, room conditions, noise and verified operating performance.

15. How to Calculate Air Purifier Room Coverage From CADR

If the purifier's particle CADR is known, users can estimate the room volume it could serve at a selected eACH target.

Formula:

Estimated Room Volume = Particle CADR / Target eACH

For example:

Particle CADR = 300 m³/h

Target = 5 eACH

Estimated Room Volume = 300 / 5 = 60 m³

If ceiling height is 3 metres:

Estimated Floor Area = 60 / 3 = 20 m²

Therefore, a purifier with a verified particle CADR of 300 m³/h corresponds to approximately 20 m² at the selected five-eACH target and three-metre ceiling height.

This is a mathematical sizing estimate, not a guarantee of actual room-level air quality.

Advertised room coverage can vary significantly depending on the assumed air-cleaning target and ceiling height.

16. Why Advertised Air Purifier Coverage Can Be Misleading

Some air purifiers advertise coverage such as:

Suitable for 30 m²

Suitable for 50 m²

Suitable for 80 m²

However, the meaning of these figures depends on the manufacturer's assumptions.

Important questions include:

What ceiling height was assumed?

What equivalent clean-air change target was used?

Was the CADR independently verified?

Was the rating based on maximum fan speed?

What pollutant was tested?

Does the advertised area include open-plan spaces?

For example, a purifier may appear suitable for 50 m² under one calculation method but provide fewer equivalent clean-air changes than a customer expects.

Compare verified particle CADR and calculate the room volume rather than relying only on a large coverage number.

17. Can Two Smaller Air Purifiers Replace One Large Purifier?

Multiple air purifiers may be used in one room.

For example:

Option A

One purifier with verified particle CADR of 500 m³/h.

Option B

Two purifiers, each with verified particle CADR of 250 m³/h.

The nominal combined particle CADR is 500 m³/h in both cases.

However, actual performance may differ because of:

Placement

Airflow distribution

Fan settings

Obstructions

Noise

Maintenance

Interaction with existing ventilation

For preliminary calculations, the rated particle CADRs may be added when the units operate simultaneously under the relevant conditions.

However, this assumes the specifications are comparable and does not guarantee uniform room cleaning.

Multiple purifiers can be useful, but their combined performance should be evaluated within the actual room layout.

18. How to Estimate the Number of Air Purifiers Required

A simplified formula is:

Number of Purifiers = Required Total Particle CADR / Particle CADR per Unit

Round the result up to a whole number.

For example:

Required total particle CADR = 600 m³/h

Each purifier CADR = 250 m³/h

600 / 250 = 2.4

Rounded up:

3 purifiers

The nominal combined particle CADR is:

3 × 250 = 750 m³/h

This provides an illustrative capacity above the selected target.

Actual requirements may differ due to existing filtration and airflow distribution.

The number of purifiers should be based on verified operating performance, not only the number of machines.

19. Why CADR May Change With Fan Speed

Many air purifiers provide multiple fan speeds.

The highest published CADR may correspond to maximum airflow.

At a lower fan speed, the purifier may deliver less clean air.

This matters for:

Bedrooms

Libraries

Offices

Classrooms

Meeting rooms

A customer may purchase a purifier based on maximum CADR but operate it continuously at a quiet setting.

The actual clean-air delivery may therefore be lower than the published maximum.

When possible, check the purifier's verified CADR at the fan setting intended for regular use.

20. HEPA Filter Efficiency vs CADR

HEPA filter efficiency and CADR describe different characteristics.

HEPA Filter Efficiency

Describes particle capture performance under specified filter test conditions.

CADR

Describes the air cleaner's tested delivery of cleaned air for a specified pollutant.

A purifier may contain a high-efficiency filter but have limited airflow.

Another purifier may have greater airflow but different filtration performance.

For whole-room particulate cleaning, the combination of airflow and particle removal is important.

A high-efficiency filter alone does not guarantee adequate CADR for a large room.

21. Can Air Purifiers Remove All Haze Pollutants?

No.

Haze may contain both particles and gases.

Suitable particulate filtration can help reduce PM2.5 and other airborne particles.

However, ordinary HEPA filtration does not remove every gaseous pollutant.

Gas-phase pollutants may require separate control measures.

Some electronic air-cleaning technologies may also generate ozone as an unwanted by-product.

For haze-related PM2.5, focus on verified particulate cleaning performance while recognising that other pollutants may require different controls.

22. How to Use Temtop S1 Up to Observe Air Purifier Performance

The Temtop S1 Up Air Quality Monitor can support general indoor PM2.5 observations.

A practical procedure includes:

Step 1 - Record Room Conditions

Document room dimensions, windows, doors and ventilation.

Step 2 - Position the PM2.5 Monitor

Place it in a representative occupied area, away from the purifier's direct air outlet.

Step 3 - Record Initial PM2.5

Allow readings to stabilise according to the manufacturer's instructions.

Step 4 - Operate the Air Purifier

Use a consistent fan speed.

Step 5 - Record PM2.5 Over Time

Record measurements at consistent intervals.

Step 6 - Review the Trend

Observe whether particulate concentration decreases.

Step 7 - Investigate Unexpected Results

Consider outdoor infiltration, indoor particle sources and filter condition.

Temtop S1 Up can help observe PM2.5 trends but cannot independently certify laboratory CADR or HEPA filter efficiency.

23. Example of PM2.5 Before and After Air Purifier Operation

The following figures are hypothetical and provided only to demonstrate monitoring records.

They are not actual Temtop S1 Up measurements.

TimeExample PM2.5Before purifier operation65 µg/m³After 15 minutes52 µg/m³After 30 minutes39 µg/m³After 45 minutes28 µg/m³After 60 minutes21 µg/m³

This example illustrates a decreasing PM2.5 trend.

However, changes may also be influenced by ventilation, particle deposition and changing pollution sources.

A portable monitor alone cannot determine the purifier's official CADR.

Use manufacturer-verified CADR for sizing and PM2.5 monitoring for observing real-world particulate trends.

24. Why PM2.5 May Remain High Despite Adequate CADR

Even a purifier with a seemingly suitable CADR may not produce the expected PM2.5 reduction.

Possible reasons include:

Continuous Outdoor Haze Infiltration

Fine particles may continue entering the building.

Indoor Smoke Sources

Smoking, cooking and other combustion activities may generate particles.

Poor Airflow Distribution

Cleaned air may not circulate effectively throughout the room.

Incorrect Fan Setting

The purifier may be operating below its rated CADR condition.

Filter Problems

Blocked or incorrectly installed filters may affect performance.

Measurement Conditions

Sensor placement, humidity and averaging periods may influence readings.

CADR is an important sizing specification, but actual indoor PM2.5 also depends on the environment and pollution sources.

25. CADR vs Ventilation - Important Differences

Air purification and ventilation are related but different functions.

Air Purification

Removes specified pollutants from air passing through a filtration system.

Ventilation

Introduces and removes air to manage indoor pollutants and provide fresh-air exchange.

A recirculating air purifier can reduce airborne particles without introducing fresh outdoor air.

Therefore, a room may have low PM2.5 but still have inadequate ventilation.

For example, carbon dioxide may accumulate in a heavily occupied room without sufficient fresh-air exchange.

Portable air purifiers should not be used as a substitute for required ventilation.

Where available, properly designed filtered ventilation can contribute to both particulate control and fresh-air provision.

26. Common CADR Calculation Mistakes

Mistake 1 - Using Floor Area Without Ceiling Height

Rooms with the same floor area may have different volumes.

Correct approach: Calculate length × width × height.

Mistake 2 - Assuming Advertised Coverage Is Universal

Coverage figures may use different assumptions.

Correct approach: Compare verified particle CADR.

Mistake 3 - Confusing CADR With Airflow

Airflow and clean-air delivery are not necessarily the same.

Correct approach: Use the specified particle CADR.

Mistake 4 - Assuming Maximum CADR Applies at Every Fan Speed

Lower speeds may provide less clean-air delivery.

Correct approach: Check operating conditions.

Mistake 5 - Ignoring Existing Ventilation and Filtration

Other systems may contribute to particulate removal.

Correct approach: Consider the full indoor air system.

Mistake 6 - Assuming More CADR Guarantees Safe Air

Indoor sources and other pollutants may remain.

Correct approach: Combine filtration with source control and appropriate ventilation.

Mistake 7 - Using PM2.5 Readings to Claim Certified CADR

Portable PM2.5 readings cannot independently establish a laboratory CADR rating.

Correct approach: Use verified CADR specifications and treat indoor monitoring as observational evidence.

27. Frequently Asked Questions

What does CADR mean?

CADR stands for Clean Air Delivery Rate and describes tested clean-air delivery for a specified pollutant.

How do I calculate air purifier CADR?

Calculate room volume and multiply it by the selected equivalent clean-air change target.

What is the formula for room volume?

Room volume equals length multiplied by width multiplied by ceiling height.

Is 300 m³/h CADR enough for a bedroom?

It depends on bedroom volume, the intended clean-air change target and operating conditions.

What is the difference between CADR and ACH?

CADR is a clean-air delivery rate. ACH or equivalent clean-air changes relate an airflow or clean-air delivery rate to room volume.

Does an air purifier provide fresh air?

A recirculating air purifier generally filters indoor air rather than introducing outdoor fresh air.

Can I combine the CADR of two air purifiers?

For preliminary sizing, comparable particle CADRs can be added when units operate simultaneously under the relevant conditions. Actual room performance depends on placement and airflow.

Can Temtop S1 Up measure CADR?

No. It can help observe PM2.5 trends but does not independently certify CADR.

Can Temtop S1 Up measure PM2.5?

Yes. It can be used for general indoor PM2.5 observations according to its supported functions.

Where can I buy a PM2.5 monitor in Malaysia?

Customers can contact MTM Precision Sdn Bhd in Puchong, Selangor, for Temtop S1 Up pricing and current stock availability.

28. Buy Temtop S1 Up PM2.5 Air Quality Monitor Malaysia

MTM Precision Sdn Bhd supplies portable air quality monitoring instruments for residential, educational, office and commercial applications throughout Malaysia.

Customers selecting an air purifier may wish to observe indoor PM2.5 concentrations before and during purifier operation.

The Temtop S1 Up Air Quality Monitor is an option for general indoor particulate monitoring.

Potential applications include:

Home PM2.5 monitoring

Bedroom air purifier observation

Office particulate monitoring

Classroom air quality checks

Haze-related indoor monitoring

Air purifier performance observation

Window closure comparisons

General indoor particulate monitoring

Customers may contact MTM Precision for:

Temtop S1 Up pricing

Current stock availability

Product specifications

Indoor PM2.5 monitoring applications

Air quality monitor comparisons

General product selection assistance

MTM Precision serves customers throughout Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kelantan, Terengganu, Kedah, Perlis, Sabah and Sarawak.

Contact MTM Precision Sdn Bhd

Showroom & Service Centre

No. 29-1 & 2, Jalan Bandar 18,

Pusat Bandar Puchong,

47160 Puchong, Selangor, Malaysia.

Tel: 03-8080 7172

WhatsApp: +6016-660 7346

Email: mtmpre@yahoo.com

Website: www.mtmpre.com.my

Want to Check Your Indoor PM2.5 After Installing an Air Purifier?

Contact MTM Precision for Temtop S1 Up pricing, stock availability and assistance selecting a suitable portable PM2.5 monitoring instrument.

You may send us your room dimensions, air purifier model, verified CADR or existing PM2.5 readings through WhatsApp for an initial recommendation.

Conclusion

Calculating air purifier CADR and room coverage helps homeowners, offices and schools make more informed purchasing decisions during haze episodes in Malaysia.

The basic method involves calculating room volume and selecting an appropriate equivalent clean-air delivery target.

However, actual particulate removal also depends on purifier placement, fan speed, filter condition, outdoor infiltration and indoor particle sources.

The Temtop S1 Up Air Quality Monitor can help users observe changes in indoor PM2.5 concentrations during purifier operation.

It does not replace laboratory CADR testing or professional ventilation assessment.

A practical air purifier selection process combines verified particle CADR, correct room sizing, effective filtration, appropriate ventilation and real-world PM2.5 monitoring.

For PM2.5 Air Quality Monitor Malaysia and Temtop S1 Up Malaysia enquiries, contact MTM Precision Sdn Bhd in Puchong, Selangor.