App icon sizes
No transparency, no rounded corners; iOS applies the mask itself.
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Design one master at 1024 × 1024 and export from it. iOS wants a square with no transparency and applies its own rounded mask; Google Play wants a 512 PNG with alpha.
How to use the app icon sizes
Android adaptive icons are the part that catches people. The launcher applies a mask that varies by device — circle, squircle, rounded square, teardrop, and only the central 66 percent of the canvas is guaranteed to survive it. So an adaptive icon has to be designed with a generous margin, with the outer quarter treated as bleed rather than as content. iOS is stricter in a different way: submitting an icon with rounded corners already applied gives you a double-rounded result, and transparency is rejected outright at submission.
Questions
Design at 1024 × 1024 and export what each store needs. iOS takes the 1024 directly; Google Play wants 512.
No. iOS applies its own mask, and pre-rounding gives a double-rounded icon.
No, it is rejected at submission. Use a solid background.
An Android icon the launcher masks into different shapes per device. Only the central 66 percent is guaranteed visible.
The adaptive mask. Keep the design inside the central two-thirds and treat the rest as bleed.