Aspect ratio
Aspect ratio is the shape of a picture or video, written as its width compared with its height, so 9:16 is tall, 16:9 is wide and 1:1 is square.
Why it matters when you post for yourself
On social media you'll meet four. 9:16 is full-screen vertical, the shape of Reels, TikTok, Shorts and stories, usually 1080 by 1920 pixels. 4:5 is a portrait feed post, 1080 by 1350. 1:1 is square, 1080 by 1080. 16:9 is wide, the shape of a YouTube video, 1920 by 1080.
The numbers are a shape, not a size: 1080 by 1920 and 720 by 1280 are both 9:16. Instagram's Help Centre says a reel can be anything from 1.91:1 to 9:16, and that a photo keeps its full resolution between 1.91:1 and 3:4.
If you film yourself, film in the tallest shape you'll need. A 9:16 video crops down to 4:5 or 1:1 as long as your face stays in the middle; a 16:9 video loses most of the frame when you crop it tall.
Example
You film a 30-second tip with your phone upright: that's 9:16, ready for Reels and TikTok. For your Instagram feed you crop it to 4:5, and for LinkedIn to 1:1, keeping your face in the middle of each.
Where it shows up in Postmosis
The video editor in Postmosis exports one video in 9:16, 4:5, 1:1 and 16:9 in one run, and face follow keeps you in frame in each. See the video editor
Related terms
Try it
Sources
- Instagram Help Centre: Reel size and aspect ratios on Instagram, read 28 October 2026
- Instagram Help Centre: Image resolution of photos you share on Instagram, read 28 October 2026
Common questions
Start my weekWhat size is 9:16 in pixels?
1080 by 1920 is the usual size for a phone video. Any width and height in the same proportion is 9:16 too, such as 720 by 1280.
Is 4:5 or 1:1 better for an Instagram post?
At the same width, 4:5 is taller, so it fills more of the screen as people scroll. Both are allowed, so pick the one your picture suits.
How do I change a photo's aspect ratio?
Crop it, keeping what matters in the middle. The free image resizer on this site crops or fits a photo to Instagram and LinkedIn sizes in your browser.
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