Fit the feed, do not invent a Story size
1:1 vs 4:5 on a phone grid
1080×1080 (captured ~2160×2160) is the classic grid tile. 1080×1350 (~2160×2700) is the portrait post that occupies more feed height. Both are real Instagram recommendations for stills. A collage of four dinner photos belongs in one of those boxes so the app is not letterboxing a 16:9 landscape into a square hole. Keep cell count low — two to four pictures remain readable; nine tiny cells become a texture when the post is the size of a thumb.
Collage vs carousel on Instagram
A collage is one image. A carousel is up to ten swipeable frames (Instagram’s cap; the studio allows sixteen slides if you ignore that). Use a collage when the point is comparison or a single “set” aesthetic. Use carousel mode — or the carousel hub — when each photo deserves full-frame and a swipe. Do not smash ten full-res portraits into one 1:1 grid and expect anyone to see expressions. Cover images for Reels are a different crop again; 4:5 is closer than 16:9, but 9:16 is the Story/Reel language and we do not fake it.
Compression and safe area
Instagram will recompress whatever you upload. Export JPG 0.92 or PNG, at least 1080 CSS pixels wide (we already capture 2×). Put faces away from the extreme edge: UI chrome and the circular profile crop on some surfaces will eat corners. Highlight icons are round — the circle clip-path layout is more honest than a square with the subject in a corner. HEIC from iPhone must be converted before the drop zone will cooperate.