Instagram re-compresses everything you upload. The way to keep your photos sharp is to hand it a file that already matches its dimensions, so it has nothing left to do. This page is preset to 1080 × 1080, the square post size.
Preset to 1080 × 1080 for feed posts. Switch to 1080 × 1920 below for stories and reels.
Instagram displays at 1080 pixels wide. Anything larger is downscaled on their servers, using their settings rather than yours.
Portrait 4:5 occupies more of the screen than square as someone scrolls, which is why most accounts that care about reach post in it.
Upload a 12-megapixel photo and Instagram has to reduce it to 1080 pixels wide, then compress it for delivery. That happens on their infrastructure, tuned for storage cost rather than for your photograph.
The heavier the file you give them, the more aggressive that pass tends to be. Hand over a file already at 1080 pixels and reasonably compressed and there is very little left for their encoder to do — so it does less, and what your followers see stays closer to what you exported.
Every compression pass throws away information permanently. Compressing an image that has already been compressed compounds the damage — this is what people mean by generation loss.
So work from your original file, not from something already exported for another platform, and definitely not from a screenshot. One resize and one compression, straight from the source, then upload.
This page presets quality to 82, which is the range where JPEG artefacts stop being visible on a phone screen while the file stays light. Below roughly 70 you start seeing blocking in skies and skin tones — precisely where Instagram's own pass will then make things worse.
For flat graphics, text overlays or illustration, push quality higher. Those have hard edges that show compression far more readily than photographs do.
1080 pixels on the long edge. Square posts are 1080 × 1080, portrait 1080 × 1350, landscape 1080 × 566, and stories or reels 1080 × 1920. Anything larger gets downscaled by Instagram anyway.
Instagram resizes and re-compresses every upload on its own servers. Giving it a file already at 1080 pixels and sensibly compressed leaves its encoder far less to do, so your image stays closer to the original.
Downscaling is the least damaging operation in image editing — you are discarding pixels that would have been thrown away by Instagram regardless. Doing it yourself means you control the result.
Compress the batch once at 1080 × 1080 for feed posts, then change the resize preset to 1080 × 1920 and run the story versions. Both take seconds and nothing is uploaded.