THE SECRET FORMULA FOR APPLE'S ROUNDED CORNERS

Summary from the TLDR Design newsletter

Apple’s products are not circular, but instead “squircles”. Squircles are complex curves that remove the discontinuity between the straight and curved sections of a surface. Apple’s line of products and their roundness scores: desktop-style devices at 0%, displays are between 2% and 3%, MacBooks are between 7% and 10%, iPads are between 12% and 18%, and iPhones are around 33%.