How Mobile Screen Size, Resolution, and PPI Screen Affect Test Coverage

Mobile screen sizes are growing bigger. And it's more important than ever to understand key device characteristics from a development and testing standpoint. This includes:

• Mobile screen size.
• Screen resolution.
• Screen PPI (pixel per inch / pixel density).

These characteristics are important whether you are developing native apps, hybrid apps, or responsive web apps. 

A Guide to Mobile Screen Size and Density

There are a variety of mobile screen sizes available. As of November 2015, tablet and mobile screen sizes range from 4.7" to 9.7". 

Common mobile screen resolutions include: 480×800, 640×1136, 720×1280, 750×1334, 1080×1920, and 1440×2560. The most common resolution is 720x1280. 

How Android Categorizes Mobile Screen Density

Android categorizes mobile screen density into one of six families: 

• LDPI (low): ~120dpi
• MDPI (medium): ~160dpi
• HDPI (high): ~240dpi
• XHDPI (extra high): ~320 dpi
• XXHDPI (extra extra high): ~480 dpi
• XXXHDPI (extra extra extra high): ~640 dpi

Source: (Perfecto's Device Coverage Index, Nov. 2015)

It's important that you don't mix devices and operating systems based on the location of the devices. And it's also important to understand that screen size and resolution can change visuals.

For example, two Samsung devices with the same screen size but different resolutions might show different visuals to the user. Or they will consume more CPU and battery to process the various app visuals on these devices.

As a starting point, it is easy to determine your device's PPI and classify it as one of the density families accordingly.

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How to Calculate PPI Screen

1. Calculate the Dp Value

Here's the formula to calculate the Dp value:

(calculate the device screen resolution square root --> for iPhone 6 it would be 750 x 1334)

So, you'll get 1,530 as the Dp value.

2. Match the Screen Size to the Dp Value

Match the screen size to the above Dp value to get the PPI.

An iPhone 6 device, which has a 4.7'' screen size, will result in 326 PPI.

Why Do Mobile Screen Size & PPI Matter?

Mobile apps run on different devices equipped with very different hardware (systems on chip). Therefore, these devices have a varied amount of CPU as well as battery types. This impacts performance.

So, loading a given app on an LG G4 (5.5'') with 515 PPI would be different from an iPhone 6S Plus (also 5.5") but with a 401 PPI. The CPU, battery usage, and performance (responsive time) would be different for each device. 

Because there is such a large, fragmented market of devices, there's a lot for developers and testers to consider. You ought to be thinking of the end user experience. And that means app performance, visuals, usability, and robustness. 

It will be critical to know your app's benchmark performance on a variety of devices. This is a good step toward having the right test coverage for your mobile app.

How to Test Mobile Screen Size With Perfecto

Testing screen size, resolution, and PPI among manufacturers should be your first step in assuring good user experience across platforms.

 Take a look at the Android OS release history below. It's clear that bug fixes around performance, battery consumption, and user interface are key. 

Another aspect of mobile screen sizes teams should incorporate in their testing is the advent of foldable phones. Teams will need to ensure their apps can correctly adjust and function with all sorts of devices with foldable screens. In 2022 alone, more than 14.2 million foldable smart phones were sold.

When you use a tool like Perfecto for mobile testing, it's easy to test for a variety of mobile screen sizes, resolutions, and PPI. You can leverage our mobile test lab to make sure that your app runs smoothly, regardless of device.

See for yourself how Perfecto can help you test screen size, resolution, and PPI. Get started with a free trial.

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• Mobile & Web Test Coverage Index
• Mobile Testing Basics
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