Every app needs its icon in many sizes, one for each screen density and one for the store listing. You design one square image and generate the rest.
Start with one good master
- A square image, at least 1024 × 1024 pixels.
- Keep the important part near the middle, so it survives rounded corners and different shapes.
- Do not add rounded corners yourself. iOS and Android round them for you.
- Do not use transparency for iOS. Apple requires an opaque icon.
What you get
- iOS: an AppIcon set from 20 up to 180 pixels, plus the 1024 pixel App Store icon, with the Contents.json file Xcode reads.
- Android: launcher icons at 48, 72, 96, 144 and 192 pixels for mdpi to xxxhdpi, plus a 512 pixel icon for Google Play.
Add them to your project
- Xcode: drag the AppIcon.appiconset folder into Assets.xcassets, replacing the existing set.
- Android Studio: copy the mipmap folders into your project res folder, and upload the 512 pixel icon in the Play Console.
Good to know
Android also supports adaptive icons made of a foreground and a background layer. The generator makes standard icons, and you can create adaptive layers in Android Studio. Store requirements change, so check Apple and Google documentation before you submit.