Which of Sume's nine aspect ratios work on Reels, Shorts, TikTok ads
Sume lists nine video aspect ratios. Checked against Instagram's 1.91:1 to 9:16 Reel range, YouTube's square-or-vertical Shorts rule and TikTok's ad ratios.
Sume's video docs list nine aspect ratios: 16:9, 9:16, 1:1, 4:3, 3:4, 3:2, 2:3, 21:9 and 9:21. Each model advertises only a subset in supported_aspect_ratios. Against three platform rules, only 9:16 and 1:1 work on all of them, and the table below shows where the others fall.
The rules are from three vendor pages, read 2026-10-03: Instagram Reel size (1.91:1 to 9:16), YouTube Shorts upload (square or vertical, up to 3 minutes) and TikTok video ad specifications (9:16, 16:9 and 1:1 for non-Spark ads). The ratio list is from the Sume videos docs.
The lookup table
Width divided by height decides the Reel column: the range runs from 0.5625 (9:16) to 1.91. The Shorts column reads "square or vertical" as width no greater than height.
| Ratio | Instagram Reel | YouTube Short | TikTok ad |
|---|---|---|---|
| 9:16 | Yes, the tall limit | Yes | Yes |
| 9:21 | No, narrower than 9:16 | Yes | No |
| 2:3 | Yes | Yes | No |
| 3:4 | Yes | Yes | No |
| 1:1 | Yes | Yes | Yes |
| 4:3 | Yes | No | No |
| 3:2 | Yes | No | No |
| 16:9 | Yes | No | Yes |
| 21:9 | No, wider than 1.91:1 | No | No |
What follows from it
- 9:16 and 1:1 are the two ratios safe everywhere, so a model that offers both gives you the most reuse.
- 9:21 and 21:9 fit none of the Reel and TikTok rules cleanly, so they are for other uses.
- A TikTok ad needs the exact pair of 9:16, 16:9 or 1:1, so 3:4 and 2:3 would need a crop or a fit mode first.
Ask the catalog, not a table
Do not hard-code which model takes which ratio. The docs say limits are not uniform, and GET /v1/catalog returns supported_aspect_ratios per model. Fetch it before you submit a generation request.
curl "https://api.sume.com/v1/catalog" \
-H "Authorization: Bearer $SUME_API_KEY"
A generation request names the ratio with aspect_ratio, for example 9:16, next to model, prompt, duration and resolution. If the model you want lacks the ratio a platform needs, generate at one it supports and reframe with Timeline's fit modes.
Sources
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