What is Aspect Ratio (9:16, 1:1, 16:9)?

Aspect ratio is the width-to-height proportion of your video or image — 9:16 is full-screen vertical (TikTok, Reels, Shorts, Stories), 1:1 is square (feed placements), and 16:9 is horizontal (YouTube, desktop).

Formula: Aspect ratio = width ÷ height (e.g. 1080×1920 = 9:16)

The mechanics

The ratio determines how much of the screen your ad occupies and whether the platform letterboxes, crops, or shrinks it. A 16:9 clip dropped into a TikTok feed plays as a small strip with black bars, surrendering most of the screen; a native 9:16 ad fills it. Ratio also changes composition rules: vertical frames favor tight, centered subjects and stacked text, while horizontal frames give room for wide scenes and side-by-side layouts.

Signals that matter

• Good: each placement gets a natively framed version — 9:16 for vertical feeds, 1:1 or 16:9 where those placements run
• Bad: one horizontal master video auto-cropped to vertical, cutting off the product or the actor's face
• Bad: letterboxed uploads (black bars top and bottom) on full-screen vertical placements

Putting it to work

Treat each aspect ratio as its own creative, not a crop of one master file — composition that works wide usually fails tall. Generating ads inside Claude with Polaris lets you specify the ratio per render and batch native versions for every placement instead of re-editing one file three times. See the full ecommerce ads glossary, or put it into practice with the Polaris AI UGC ad generator.