9:16 aspect ratio

The ratio is exactly the reciprocal of 16:9, so a 1080 by 1920 frame contains precisely the same number of pixels as a 1920 by 1080 one. That symmetry makes encoding budgets and file size estimates transfer directly between the two, and it makes nothing about the composition transfer at all.

The important caveat is that 9:16 is a video standard, not a hardware description. Phone displays moved past it years ago and are now commonly around 19.5:9 or taller, which in the vertical direction is nearer 1:2.17. A 9:16 asset shown full screen on such a device is either letterboxed at top and bottom or cropped at the sides.

That is why platform safe areas matter more here than on any other canvas. The frame is a fixed 9:16 but the visible portion of it varies by device, and the interface overlays vary by platform, so the reliable design region is a rectangle in the middle rather than the whole frame.

For stills, the cropper offers a 9:16 ratio and the social post generator composes at 1080 by 1920 directly. Both produce the standard frame, and neither can tell you where a given platform's draws its controls on top of it. That part has to come from a test on a real device, because it changes with application updates and with the shape of the handset.