Correct size of tab bar icons in iOS?

Question

iOS

I want to make several icons for a tab bar under iOS 11. For example, I downloaded icons from other authors from the Internet, which are supposedly sharpened for iOS, but they are all made in perfect rectangles, although even with the naked eye you can see that standard Apple applications have different icons width and height.
I came across style guides , but there was more confusion. At x1 size, it is impossible to make it pixel perfect.

Answer 1

You must have misunderstood the guidelines. Tell us where you got 23x20 and 31x28 from, I'll try to help. It looks like they've got it all covered up. If you have an @1x layout, as many do, then you are interested in the values ​​in parentheses. For example, Target width and height (circular glyphs) 75px × 75px (25pt × 25pt @3x) means 25x25 pixels in your layout.