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Xiaomi Smart Air Purifier 4 Compact Review

Derek Hales

Written By: Derek Hales

Updated on:

Compact, quiet, and Effective

Xiaomi Smart Air Product Description

 Xiaomi Smart Air Purifier 4 Compact

The Xiaomi Smart Air Purifier 4 Compact is the smallest air purifier Xiaomi makes, but it still has many of the same features and connectivity options as the big boys. Its quiet operation makes it well suited to the small rooms, as does the 158 sq. ft. coverage area. If you’re looking for an effective, small-room air purifier, this is a great option.


  • Excellent air purifying performance. It achieved a PM2.5 of 0.1 and PM10 of 0.2 during our tests.
  • Useful settings such as sleep mode, child lock, and more can be accessed via smart app that has 4.2 review average
  • Extremely quiet even on its highest setting reaching a maximum decibel level of 42.8


  • Small coverage area at only 158 sq ft.
  • Manual settings only accessible via smart app
  • Measurement of post-test AQI was good but a higher lower than average


Quiet, but deadly (to particulates)
  • Design - 96%
  • Performance - 98%
  • Quality - 97%
  • Usability - 96%
  • Value - 94%


The Xiaomi Smart Air Purifier 4 Compact is the smallest of 4 versions of Xiaomi series 4 air purifiers. Its performance is fantastic during our tests with it reducing PM2.5 to 0.1 and PM10 to 0.2. Although its coverage area is only 158 square feet, it is the compact version with a 14-inch height and 8 each diameter. Overall it is light, quiet, and highly effective.

In This Review

Purification | Filters | Noise | Usability | Size | Specs | Summary

Purification Performance

To test the Xiaomi Smart Air Purifier 4 Compact, we set up the air purifier in a medium-sized room in our office. I took a baseline measurement before starting the test to measure the current air quality.

Then, I let the Xiaomi 4 Compact run on the highest setting for 1 hour and then measured the air quality to get another set of measurements.

Xiaomi Smart Air Compact Tabletop Purifier
Xiaomi Smart Air 4 Compact on countertop

After letting it run for 1 hour, we take another measurement of the air quality and compare it to the baseline data. From that comparison, we can analyze the purification performance of the Xiaomi 4 Compact. 

Starting Baseline

  • PM2.5: 3.6
  • PM10: 5.7
  • Particles: 724
  • AQI: 15

After 1 Hour

  • PM2.5: 0.1
  • PM10: 0.2
  • Particles: 19
  • AQI: 2

Avg – All Purifiers

  • PM2.5: 0.47
  • PM10: 0.70
  • Particles: 54.96
  • AQI: 1.76

The Xiaomi Compact improved PM2.5 air quality to 0.1 and PM10 to 0.2 in the medium-sized room we tested in (~14’x10’).

As we are always looking for numbers as close to 0 as possible, these are fantastic results.

Air Quality Testing meter
Air Quality Testing meter

On average, we see air purifiers achieve a PM2.5 of 0.47 and a PM10 of 0.70 after our 1-hour test. The Xiaomi 4 Compact performed significantly better in these readings.

Particles were also reduced to a much lower number than average.

However, the Compact’s AQI reading after the one-hour test was actually a bit higher than average performance across all air purifiers tested to date. Though, a measurement of 2 is still undoubtedly a good AQI reading.

Xiaomi Smart Air Compact Powered On
Xiaomi Smart Air 4 Compact powered on

In order to get these measurements, we used the Temtop LKC-1000S+ professional air quality detector.

Below is a chart that gives some references for good vs. bad air quality.

air quality index - PM 2.5 particulate matter index

Ozone Test

We tested the Xiaomi 4 Compact with an electronic ozone meter to determine if any measurement level of ozone is created by the purifier.

In our tests, no measurable amount of ozone was created. Our ozone meter measures to a resolution of 0.1 parts per million.

The Filters

The Xiaomi 4 Compact uses a single, 3-in-1 proprietary filter in its housing.

Notably, the filter is modified from the standard HEPA designation into something unique to Xiaomi. They call it “Xiaomi’s High Efficiency Filter.”

Xiaomi Smart Air Compact HEPA Filter Size
Xiaomi Smart Air 4 Compact size of HEPA filter

They claim that it can clean better, use less energy, and is quieter than the standard HEPA filter.

The 3 elements in this filter include:

  • Pre-filter
  • HEPA Equivalent
  • And activated carbon

One of the biggest differences in this filter is that it has larger spaces between the fibers so more air is able to pass through the system.

Noise Test

We also tested how loud the air purifier was while running. To perform this test we ran the air purifier on the three different modes and use a sound meter to measure noise level. Afterward, we tested the Xiaomi 4 Compact Smart Purifier from about 3’ away.

Our results showed the following decibel levels from each mode.


38.9 dB

Lowest Setting

39.1 dB

Highest Setting

54.2 dB

These decibel recordings confirm that this is a quiet air purifier. With a maximum reading of only 54.2, our reference chart would say it is about equal to a refrigerator, moderate rainfall.

That is using the highest setting. On its lowest setting – sleep mode – it was barely distinguishable from the regular, ambient noise of the room.

Xiaomi Smart Air Compact with HEPA filter removed
Xiaomi Smart Air 4 Compact fan exposed

This would be more than suitable for a child’s bedroom or other small room.

Common noise levels:

  • 20 dB – rustling leaves
  • 30 dB – whisper
  • 40 dB – quiet library, babbling brook
  • 50 dB – refrigerator, moderate rainfall
  • 60 dB – normal conversation, dishwashers
  • 70 dB – traffic, showers
  • 80 dB – alarm clock, telephone dial tone

Usability Tests

The usability on the Xiaomi Smart Air Purifier 4 Compact is quite good. There are few moving parts, intuitive touch controls, and smart home connectivity. Maintenance is also kept simple with only one filter to manage. Manual speed controls are somewhat limited to the complimentary “Mi” app


Setup on the Xiaomi 4 Compact is as easy as unboxing, finding a spot 8 inches away from other solid options, and plugging it in.

There are some pieces of plastic packaging around the outside of the purifier that you will need to make sure are removed before use.

Xiaomi Smart Air Compact Power Cord
Xiaomi Smart Air 4 Compact power cable

This whole process takes less than 5 minutes for a single person. 


Controls on the Xiaomi 4 Compact are accessed via the LED touch display on the top-middle of the device and through app connectivity.

Xiaomi Smart Air Compact buttons and indicators
Xiaomi Smart Air 4 Compact buttons and indicators

Touch settings/indicators found on the display include:

  • Light Adjustment 
  • Child lock indicator 
  • Wi-Fi indicator
  • Replace filter indicator
  • Power button
  • Air quality light indicator
  • Mode indicator
  • Mode switch

The modes that you can cycle through are Automatic, Manual, and Sleep. Automatic changes the air purifiers speed based on need resulting from indoor air quality gathered from a built-in sensor. Sleep merely sets the speed to the lowest and turns nearly all indicator lights off.

Child lock is easily enabled by holding down the button and you will see the display light up the closed lock symbol to indicate its use.

Subjectively speaking, the app is well-developed compared to most companion apps for smart products.

Xiaomi is a large brand with many different types of products that all use this app. It would make sense that they invested a decent amount of time and effort to make it usable.

Xiaomi Smart Air Compact Using App
Xiaomi Smart Air 4 Compact PM2.5 reading
Xiaomi Smart Air Compact Using App
Xiaomi Smart Air Compact app settings

The manual mode allows you to adjust speed and view various data not available on the built-in display screen.

Connecting to Wi-Fi was fairly straightforward and easy. I found the extra settings the app provides to be interesting, but not altogether necessary for a small room air purifier like this.


Xiaomi designed the Smart Purifier 4 Compact to be simple to maintain. Maintenance can be broken down into the following steps:

  • Resetting the filter
  • Replacing the filter
  • Cleaning the filter
  • Cleaning the sensor

Xiaomi suggests resetting the filter after long periods of it on standby. This is done by holding down the power button until it beeps.

The filter is recommended for replacement after 6 months to up to a year, depending on use. There is only a single cylindrical filter to replace accessible via the bottom twisting handle. 

Xiaomi Smart Air Compact Filter Access
Xiaomi Smart Air 4 Compact filter access
Xiaomi Smart Air Compact Replacling Filter
Xiaomi Smart Air 4 Compact replacing filter

As with most air purifiers, it is also recommended to vacuum or wipe large dust amounts when visible around the grate.

Finally, if you notice sensor data seems off on the app or the auto mode behaving erratically, you can clean the sensor accessed by the small flap on the back middle of the device.

Size & Dimensions

As the name suggests, the Xiaomi 4 Compact is quite small. 

Xiaomi Smart Air Compact Light Weight
Xiaomi Smart Air 4 Compact held up

Here are the exact dimensions of the Xiaomi Smart Air Purifier 4 Compact:

  • Length – 8.6”
  • Width – 8.6”
  • Height – 14”
  • Weight – 4.8 lbs

At 4.8 lbs and 8.6” wide, it is suitable for the floor or most elevated surfaces. However, Xiaomi does recommend it has 8” of clearance from a wall.


ModelSmart Air Purifier 4 Compact AC-M18-SC
Weight4.8 lbs
FiltersHEPA, Carbon, Pre-filter (Xiaomi’s High Efficiency Filter)
Wifi CompatibleNo
Room Coverage158 sq. ft.
CADR230 cfm
ReturnsVaries by retailer
Warranty1 year
PriceCheck Price

Should you buy the Xiaomi Smart Air Purifier 4 Compact?

I would recommend the Xiaomi Smart Air Purifier 4 Compact if you’re looking for the following features:

  • Quiet operation: Even at its highest setting, we measured a maximum decibel level of 42.8. This is extremely quiet and suitable for most environments. Sleep mode is better by only reaching a maximum decibel level of 30.9. There should be no issue with the Xiaomi 4 Compact in a small room.
  • Fantastic air purification performance: We measured a reduction of PM2.5 to 0.1 and PM10 to 0.2 during our performance tests. We are always looking for results as close to 0 as possible. These are about as good as you can get.
  • Lots of useful features: This is a smart purifier that comes with the Xiaomi companion app. The app runs smoothly and provides access to manual settings and air quality data. The Xaiomi is also compatible with Google Home and Alexa.

For more information or to buy the Xiaomi 4 Compact, click here. 

About Derek Hales

Derek HalesDerek Hales is the Founder and Editor-in-Chief of He has been featured in Fast Company, Reader's Digest, Business Insider,, She Knows, and other major publications. Derek has a Bachelor's Degree in Business Administration from Kansas State University. Hales has been testing and reviewing products for the home since 2014.