How many inches of screen diagonal Xiaomi Mi 9: a full analysis of the characteristics and comparison with competitors

The Xiaomi Mi 9, released in 2019, has become one of the brand’s most discutible flagships — its AMOLED screen and HDR10 support are still considered the benchmark for many users. But when it comes to accessories, protection or comparison with other models, the first question that arises is: how many inches does the Xiaomi Mi 9 have? The answer seems simple, but in practice there are nuances — from the physical diagonal to the “useful” screen area with the notch for the front camera.

In this article, we will not only give an accurate answer to the question of screen size, but also analyze how this characteristic affects the experience of use. You will learn why the Mi 9 with a diagonal of 6.39 inches feels more compact than some competitors with similar parameters, how to choose the right case or protective glass, and how its screen differs from the Mi 9T or Mi 9 SE.

If you're planning to buy or you're already the owner of this smartphone, the information below will help you avoid common mistakes, like many users mistakenly thinking that the screen size is the same as the body size, and then wondering why the 6.4-inch case is not tight.

Official data: the exact screen diagonal Xiaomi Mi 9

According to the technical specification from Xiaomi, the Mi 9 is equipped with a display with a diagonal of 6.39 inches, this figure is indicated in all official sources, including the manufacturer’s website, documents for regulators (for example, FCC ID), and even on the device box.

The Mi 9 uses a waterdrop notch for the front camera, which reduces the useful area slightly, and if you measure the diagonal of the active zone alone (excluding the cutout), it will be approximately 6.35-6.37 inches, a difference that is negligible for everyday use, but can be critical when choosing protective accessories — especially if they are designed for a clean screen without cutouts.

By comparison, the Mi 9T (released later that year) has a declaration screen diagonal of 6.39 inches, but the retractable camera has a larger display area of about 6.38 inches, which explains why some users note that the Mi 9T “seems more spacious” at the same claimed numbers.

⚠️ Warning: Don’t confuse the screen diagonal with the body dimensions! The size of the Mi 9’s 6.39-inch display doesn’t mean that the smartphone will be comfortable lying in your hand as a device with a diagonal of 5.5-6.0 inches. Due to the minimal frames, the real width of the case is 74.67 mm - this is almost like some "phablets" of 2018.

How the screen diagonal is measured: myths and reality

Many users mistakenly believe that the screen diagonal is the distance from one corner of the matrix to the opposite, measured on the outside of the smartphone.

• 📏 The frame of the body is not taken into account - even if they occupy 1-2 mm on each side.
• 🔍 The cutouts and roundings of corners (like the Mi 9) do not reduce the declared diagonal, but reduce the usable area.
• 📊 The aspect ratio (Mi 9 – 19.5:9) affects the perception of size: a narrow and long screen can “appear” larger than a wide screen with the same diagonal.

Interesting fact: in 2019, Xiaomi experimented with marketing labels, such as the Mi 9 being marketed as a 6.4-inch smartphone in some regions, even though the real diagonal was 6.39 inches, and this was due to rounding to make it easier to see, a practice common among manufacturers (for example, the Samsung Galaxy S10e had a 5.8-inch diagonal, but was often referred to as a 5.9-inch diagonal).

To independently check the diagonal, you can use the mathematical method:

1. Measure the width and height of the screen (only the active area!) in centimeters.
2. Put each value in a square and add the results.
3. Extract the square root from the sum – this will be the diagonal in centimeters.
4. Transfer centimeters to inches, dividing by 2.54.

For the Mi 9 with an aspect ratio of 19.5:9 and a diagonal of 6.39 inches, the screen width is approximately 6.8 cm, and the height is 14.2 cm.

Comparison with other Xiaomi models: Mi 9 vs Mi 9T vs Mi 9 SE

To better understand how big (or compact) the screen is, compare it to other popular models of the 2019 lineup: All three smartphones — Mi 9, Mi 9T and Mi 9 SE — were positioned as flagships, but had different approaches to design and ergonomics.

And you can see from the table that despite the same diagonal, the Mi 9T has a slightly more compact body due to the lack of a cutout. And the Mi 9 SE, despite the smaller screen, has a higher pixel density (432 PPI vs. 403 PPI in older models), which makes the picture clearer. Interestingly, the Galaxy S10 with a diagonal of 6.1 inches is narrower than the Mi 9, thanks to its narrower bezes and different aspect ratios.

If you want a compact, but you need a big screen, look at the Mi 9T, which offers the same diagonal, but without a cutout, which visually increases the usable area. And if the priority is single-handed use, the Mi 9 SE with a 5.97-inch screen will be the best choice, despite the smaller diagonal.

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The Mi 9 and Mi 9T have the same diagonal (6.39) but different designs: the Mi 9T does not have a notch due to the retractable camera, which makes its screen more spacious.

How the screen diagonal affects the choice of cover and protective glass

Knowing the exact screen size of the Xiaomi Mi 9 is critical when buying accessories. Many manufacturers of covers and glasses specify the size of the display (for example, "for 6.3-6.4 inches"), but this does not guarantee a perfect fit.

• 🛡️ Security windows: Look for models marked "for Xiaomi Mi 9" or "6.39" with waterdrop notch. Universal glass "6.4 inches" may not fit due to a mismatch of the cutout under the camera.
• 📱 Covers: Even if the cover is designed for diagonal 6.39 Inch, check if it is suitable for the exact dimensions of the body (157.5 × 74.67 × 7.6 Some Mi covers 9T may be suitable, but often differ in the location of the cutouts for the buttons.
• 🔧 Universal accessories: Holder fasteners or cardholders designed for “6.0-6.5-inch smartphones” are usually suitable, but can block access to the connector USB-C dynamic.

Pay special attention to the rounded corners of the screen on the Mi 9. Many cheap protective glasses do not cover them completely, leaving gaps, which increases the risk of chipping. 3D-A good example of a reliable brand is Spigen, Nillkin or original accessories from Xiaomi.

⚠️ Note: If you are buying a case with wireless charging support, make sure it is Qi-compatible and does not exceed 3-4 mm thick. Mi 9 supports wireless charging up to 20 watts, but some thick cases can block the signal.

Before buying accessories, check the reviews of other owners of the Mi 9. For example, on AliExpress or Amazon, there are often complaints that the glass for the “6.4-inch” smartphones are not suitable due to a mismatch in the cutout.

The exact match of the model (Mi) 9, Not Mi. 9T/SE)|

Availability of camera cutouts, speaker and connectors|

Support for wireless charging (if needed)|

Materials (TPU Polycarbonate for better protection)|

Reviews of landing (whether there are backlashes or button clamps)-->

Side ratio and resolution: why it matters for the Mi 9

Screen size isn't the only thing that affects your perception of size. Equally important is the aspect ratio and resolution. The Xiaomi Mi 9 has a ratio of 19.5:9 and a resolution of 2340×1080 pixels (Full HD+).

• 📺 19.5:9 is an elongated format that makes the smartphone visually narrower than models with a ratio of 18:9 or 16:9. For example, when watching a video at 16:9, there will be black fields on the sides.
• 🔎 Full HD+ (2340×1080) — It's not exactly standard Full. HD (1920×1080). There are more pixels vertically, which improves text clarity and interface detailing.
• 🎮 Games and apps: Not all games are optimized for 19.5:9, PUBG Mobile or Call of Duty can crop or leave black fields.

For comparison, the iPhone 11 (released in the same year) has an aspect ratio of 19.5:9, but the screen diagonal is smaller at 6.1 inches. while the Mi 9 has a higher pixel density (403 PPI vs. 326 PPI on the iPhone 11), which makes the picture more detailed.

If you watch videos or play games frequently, please note that:

• 🎬 YouTube and Netflix automatically adjust to the 19.5:9 ratio, but some 4:3 or 16:9 videos will be displayed with fields.
• 📱 Social media (like Instagram or TikTok) is optimized for vertical use, so on the Mi 9, content will occupy almost the entire screen.

If you want maximum media screen area, consider 20:9 or 21:9 models (like the Xiaomi Mi 10 Ultra), but the Mi 9 remains one of the most balanced options for those who value both multimedia and compactness.

Frequent mistakes when choosing a smartphone by screen size

Many shoppers are only looking at the screen diagonal, forgetting other critical parameters, and here are some common mistakes that lead to disappointment after purchase:

1. Ignoring the body size. For example, the 6.39-inch Mi 9 is 74.67 mm wide, which is more than the 6.1-inch iPhone 12 Pro (71.5 mm) and if you have small hands, it can be uncomfortable for single-handed use.
2. Ignoring cuts and rounds. The 6.39 inch diagonal of the Mi 9 includes a drip cutout that eats up some of the usable area. If you care about maximum viewing, look for models without cutouts (for example, the Mi Mix 3 with a retractable camera).
3. Screens with 19.5:9 or 20:9 are visually narrower than 18:9, which can be inconvenient for watching video in standard format or reading books.
4. Trust in universal accessories: 6.4-inch covers and glass are often not suitable due to differences in the location of cameras, speakers or sensors.

To avoid these errors, follow a simple rule: always check the actual dimensions of the body (width, height and thickness), not just the screen diagonal.

• Mi 9: 6.39", housing 157.5 × 74.67 × 7.6 mm.
• Mi 9 Lite: 6.39", housing 156.8 × 74.5 × 8.7 mm.

It would seem that the diagonals are the same, but the Mi 9 Lite is 1.1 mm thicker and has a different rear design, which affects the choice of cases. IPS-matrix AMOLED, What changes the perception of colors and contrast.

⚠️ Warning: If you buy the Mi 9 handheld, check the screen for burn-in, a typical problem for your Mi 9. AMOLED-To do this, open a monochromatic image (for example, a white background) and see if traces of static interface elements (for example, navigation panels) are visible).

FAQ: Answers to popular questions about the screen Xiaomi Mi 9

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If you watch videos on the Mi 9 often, try turning on Read mode in the screen settings (Settings → Screen → Read mode) which reduces the blue component of light, reducing eye strain during long-term viewing.