Redmi K40S In-Depth Review: How Much Perfect it is?


The Redmi K40 series, which has been guarding the door for a whole year, must be nominated. Excellent Samsung E4 AMOLED flagship straight screen, Snapdragon 870 + LPDDR5 memory + UFS 3.1 flash memory performance three-piece set, such a quasi-flagship configuration, but also pulled the price to less than 2000 yuan, even today can still be called “Really fragrant machine”, it can be seen how good it is. With the recent release of the Redmi K50 series, the K40 series has also blossomed, bringing us a refreshing Redmi K40S, which has been upgraded in four aspects, and the price is even lower. Now, we have received the Redmi K40S in bright black color matching, 12GB+256GB version.

Since it is a “flagship welding doorman”, extreme stacking is also a tradition of Redmi. This K40S brings a new design while inheriting the classics.

The flagship AMOLED straight screen is made of Samsung E4 material, the “performance iron triangle” is composed of Snapdragon 870 + LPDDR5 memory + UFS 3.1 flash memory and the 4500 mAh battery are fully retained.

In terms of upgrades, first, it brings the same appearance design and color matching as the K50, adopts the most popular straight-edge middle frame design, and the body is thinner and lighter.

The rear camera pixels remain the same, but with the addition of OIS optical image stabilization, which is missing from the K40, even many high-end cameras of three or four thousand yuan may not have it, which ensures that the shooting rate will be extremely high.

At the same time, the liquid-cooled copper tube becomes 3112 square mm VC liquid-cooled heat dissipation, and the area is increased by 400%, which can bring a better heat dissipation effect.

The fast charge has also been upgraded from 33W to 67W, which further shortens the charging time.

Now, let’s take a look at the performance of this upgraded version of K40 – Redmi K40S. The following picture shows the specific parameters:

Design & Appearance

The front of the Redmi K40S uses a 6.67-inch Samsung E4 luminous AMOLED flagship straight screen with a resolution of 2400×1800, supports 120Hz refresh rate, 360Hz touch sampling rate, a contrast ratio of 5 million:1, supports HDR+, MEMC frame rate compensation, the peak brightness is up to 1300nit, and the global brightness is up to 900nit.

The surface is made of wear-resistant and drop-resistant Corning Gorilla Glass 5, the screen opening is 2.76mm, and a 20 million front camera is inserted to support AI beauty and other features.

The back design of the Redmi K40S is the same as that of the K50 series. The whole is very simple, with a distinctive square and round collision design, which is different from the language design of the Redmi K40.

The Redmi K40S rear camera consists of a 48-megapixel main camera lens + 8-megapixel ultra-wide-angle lens + 2-megapixel macro lens. The entire module is in a two-stage ladder shape, and the bottom half is the fill light and 48MP OIS logo.

One of the upgrade highlights of the Redmi K40S is the use of a rounded appearance instead of a trendy small standing edge design, which looks a lot tougher, but the edges have been rounded excessively, so it will not look awkward when you hold it in your hand.

The physical buttons are on the right side of the phone, the volume up and down buttons are on the top, and the power button that supports fingerprint recognition is on the bottom.

In partial details of the top and bottom, in addition to the regular USB-C interface and SIM card slot, the Redmi K50 also supports dual speakers and infrared. The Redmi K40S comes with a 67W charger in the box.


The Redmi K40S is powered by Qualcomm Snapdragon 870. As a gaming god U, this processor takes into account both power consumption and performance. It is one of the most popular chips on the market, and even many tablets are using it.

The specifications of this chip are based on the 7nm process. The CPU consists of 1 3.2GHz super core + 3 2.42GHz large cores + 4 1.8GHz small cores. At the same time, it forms a performance three-piece set with LPDDR5 memory + UFS3.1 flash memory.


AnTuTu scored 723322 points, which is the performance of the regular Snapdragon 870, surpassing 66% of users.

Among them, the CPU score is 194831 points, the GPU score is 241428 points, the memory score is 130842 points, and the UX score is 156221 points.

Master Lu

Master Lu scored 844046 points, but it is a bit exaggerated to exceed 99% of the mobile phones.

The CPU score is 284,593 points, the GPU score is 323,309 points, the memory score is 102,540 points, and the storage score is 133,604 points.


We chose GeekBench 5, a relatively mainstream processor benchmark software in the market, for testing, and the scores given are 1029 for single-core and 3384 for multi-core.

GFXBench The performance of GFXBench, in terms of performance, belongs to the expected performance of the Snapdragon 870 GPU, which is quite satisfactory.


In Androbench, the measured sequential read speed is 1578MB/s, which belongs to the performance of UFS 3.1 flash memory

From the above results, the performance of Redmi K40S and K40 is not much different. Under the condition of mature performance tuning of Snapdragon 870, there is not much room for further digging.

Of course, the mature power consumption adjustment level and stable flagship performance release ability of Snapdragon 870 also make this chip enduring, and it is still the “most fragrant” chip on the market.

Game Test

Ace Warrior

In “Ace Warrior”, we changed the game’s picture quality and frame rate to the highest, allowing automatic reduction of picture quality and frame rate to be turned off.

During the last battle, the frame rate was basically maintained at 120 frames, which was very stable. Excluding the frame rate fluctuations caused by death, the average frame rate was 115 frames.

QQ Speed

In “QQ Speed”, we changed the game’s image quality settings to ultra-high, the intra-office frame rate and the out-of-office frame rate to very high, the resolution to ultra-clear, and the special effect level to high.

In the quick match multiplayer game, the overall frame rate is above 122 frames, although the period fluctuates, the average frame rate is also 120 frames.


If you want to understand the performance release and tuning ability of the mobile phone, it is most suitable to use “Yuanshen” to test.

We changed the game image quality to very high quality and the frame rate to 60fps. During the “Genshin Impact” game, we randomly fought monsters and ran pictures for 15 minutes in multiple scenes.

After entering the game, the initial frame rate is 55 frames, but as the game gradually heats up, the frame rate gradually decreases further, and the second half is basically stable at 48 frames.

At the same time, we detected through the infrared thermal imager that the temperature of the SoC area of ​​the mobile phone came to about 42°C.

For the above mainstream games, the performance of Redmi K40S can run smoothly, but from the experience of “Genshin Impact”, the game scheduling is slightly conservative. This should be the trade-off between heat and performance of Redmi K40S. It is recommended that players Appropriately lower the picture quality for the best gaming experience.


The rear camera of the Redmi K40S is a solution consisting of a 48 million main camera lens + 8 million 119° ultra-wide-angle lens + 2MP macro lenses.

Among them, the main camera is Sony IMX582, a 1/2″ sensor, f/1.79 large aperture, and the OIS optical image stabilization that K40 lacks is also supplemented on K40S.

Let’s take a look at the photo effects of the Redmi K40S:

In the case of sufficient light, the IMX582 main camera lens with OIS optical image stabilization has obvious advantages, the picture is transparent and bright, and the color performance is more pleasing.

After adding optical anti-shake, it can effectively reduce the blur of the picture, improve the filming rate, and no longer worry that the photos taken by handshaking will be “smeared” when taking pictures.

However, the ultra-wide-angle lens has obvious chromatic aberration and inconsistent white balance, so it is recommended to use the main camera.

Although the macro pixel is only 2 million, it has obvious advantages when shooting small natural scenes such as flowers and green plants, especially the white flowers on the top, the lines and stamens can be clearly displayed.

In terms of night scenes, the Redmi K40 controls both neon lights and architectural lights very well. At the same time, it can restore the details and color atmosphere of objects. Even in the face of complex text lighting effects, it can stabilize and control, and there is basically no glare. .

Of course, it is recommended to avoid strong light and complex lighting environments as much as possible when taking pictures, otherwise, ghosts and halos may appear in the proofs.


The Redmi K40S has also been upgraded from 33W to 67W fast charging and has a built-in 4500mAh single-cell battery.

Charging test

We started charging from 5% of the battery, charged to 47% in 20 minutes and entered the protection charging mode after 80%, the speed slowed down significantly, and it took a total of 40 minutes to fully charge.

Battery life test

For the battery life, we use the professional battery life test tool – the battery dog ​​produced by Kuai Technology to test.

For the test items, we chose the limit battery endurance test, and checked all test items including CPU high voltage, CPU multi-threading, AI recognition, picture browsing, video playback, and web browsing, simulating real usage scenarios and restoring the real load to the greatest extent. Infinitely close to the real power consumption.

We set the manual brightness to 50%, and from full blood to shut down, it took a total of 8 hours and 2 minutes, which is in line with the expected results of the Snapdragon 870 model equipped with a 4500mAh battery. According to the usage habits of ordinary users, it can be used intermittently for a day without a problem.

Read Also: Redmi K50 Pro Review: Affordable Killer Gaming Phone


On the whole, the Redmi K40S can be said to be a “hybrid” of the K40 and K50, and it still maintains a very high level of “welding doorman” quasi-flagship machine.

In terms of appearance, it is naturally consistent with the design language of the K50, but it is different, and it is also different from the K40. The different shapes also bring freshness to consumers.

Although it adopts a straight-edge shape, the Redmi K40S has also optimized the hand feel, and the edges of the fuselage have been rounded excessively, so it is very comfortable to hold in the hand.

What is even rarer is that with the change of shape, the thickness of the Redmi K40S is only 7.7mm and the weight is only 195g, which is even slightly thinner and lighter than the K40.

The performance of the Snapdragon 870 + LPDDR5 memory + UFS 3.1 flash memory quasi-flagship is naturally needless to say. Although the chip tuning is a little conservative, the performance and power consumption of the Snapdragon 870 have been witnessed.

As the most popular chip on the market, coupled with 3112 square millimeters of VC liquid cooling, even if users play games with high loads such as “Genshin Impact”, the maximum chip area is only 42 degrees Celsius, and the fuselage is controlled at a reasonable temperature. within the range, allowing players to play the game more lastingly.

The Redmi K40S is also one of the few models with a high-quality AMOLED flagship straight screen. The 120Hz high refresh rate and 360Hz touch sampling rate that can enhance the gaming experience are not absent. It also supports Dolby Vision and HDR10+ high dynamic range display. Then Atmos dual speakers. In-game or film and television experience, this Redmi K40S can bring users excellent visual enjoyment.

OIS optical image stabilization is a surprise among surprises, let alone mobile phones of the same grade in the market, even higher-end products are rare. The actual experience is day or night, no matter whether it is long-range or macro, you don’t have to worry about handshaking.

There is also an upgraded 67W fast charge, which can charge the 4500mAh battery to 50% in 10 minutes, can be fully charged in 40 minutes, and can also provide 8 hours of use time under high load.

It can be said that Redmi K40S has no shortcomings in terms of screen, performance, photography, fast charging, and other aspects. After the upgrade, it is even cheaper, starting at only 1799 yuan. It is no wonder that it is out of stock as soon as it goes on sale. Such a god-level price/performance ratio, what are you waiting for?

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