Standard in-feed is 1038x588 (approx 1.77:1 ratio, aka 16:9).
I've seen other sizes, but it always seems to work out to about the same ratio.
Close pixel ratios:
According to this tweet, the other ratios are:
- Two images: 7:8
- Three images: 7:8 first image, 7:4 for 2nd and 3rd
- Four images: 7:4, for all four images
This is another good Twitter thread on the topic. Based on this thread:
If avoiding compression:
- Use JPG instead of PNG, since Twitter will then likely avoid recompressing further
- Limit file to 5 MB max, and 4096px (either width or height)
They have started applying smart-cropping (looks like through Cloudinary), which tries to fit in box of 1000 x 420