What aspect ratio do Instagram Stories and Reels use?

Meta's guidance for Reels image ads is to leave roughly 14 percent at the top, 35 percent at the bottom and 6 percent on each side clear of text, logos and other key elements, because the interface sits over those areas.

If your image is 4:5 or square, Instagram fills the rest of the screen with a background, so a dedicated 9:16 version looks more deliberate.

To turn a wide or square image into 9:16 you can crop it, which needs room above and below the subject, or extend it with new area at the top and bottom. See Should I crop or extend an image to change its aspect ratio?.