Map the three boxes onto the timeline you actually post to
Tall discovery vs wide video stills
Pinterest still rewards tall pins. 4:5 (1080×1350 CSS) is the closest box we ship to the classic 2:3 pin; it is not 1000×1500, and a 2:3 crop after export is honest if the pin product is the job. YouTube thumbnails are 1280×720 (16:9). Our 16:9 canvas is 1920×1080 CSS (~3840×2160 captured) — larger than the thumb spec, which is what you want before YouTube’s compressor. TikTok and Reels covers are 9:16; we do not have that preset. A 4:5 board will be padded or zoomed. Do not title a 4:5 export as a “TikTok collage size.”
Professional feeds and chat apps
LinkedIn posts tolerate 1:1 and 1.91:1-ish wides. Square is the safe collage; 16:9 is the article-header cousin. WhatsApp status is closer to 9:16 — again, not our preset — while a chat image can be square without drama. X/Twitter stills in-feed often display near 16:9; 1200×675 is a common working number, and our 16:9 export downscales cleanly. Discord and Reddit will show whatever you upload; square collages avoid the “tiny panorama” problem in crowded channels.
Do not rebuild seventeen times if one ratio serves three apps
A 1:1 merch grid can go to Instagram, a LinkedIn update, and a WhatsApp broadcast. A 16:9 team still can be a YouTube thumb and an X image. Export once, then resize only if a CMS rejects the byte weight (compressor spoke) or needs an exact pixel box (resizer spoke). The failure mode is designing a “Pinterest collage” at 1:1 and wondering why it looks stubby in the pin feed — that is a mapping error, not a missing filter.