Every platform crops your picture to its own shape. Deciding that crop yourself is the difference between a clean post and one with someone's head cut off.
Choose a shape for the intended placement, such as the square or story preset, then crop the subject to that shape. Platforms may apply an additional crop and their specifications can change. Inspect the destination's upload preview before posting.
Locked resizing keeps each image's proportions. Fixed dimensions can stretch images; crop to the required ratio first.
The encoder creates a new file. Upscaling cannot recover detail that the original did not contain.
The social square preset is 1080 by 1080 pixels and the story preset is 1080 by 1920. These are shapes as much as sizes. A landscape photo forced into either will be stretched, so crop it to the shape first with Crop & rotate and then apply the preset.
Platforms change the sizes they prefer from time to time, so treat the preset as a good default and check the platform's current guidance if the exact figure matters. A larger size is rarely a problem, because platforms shrink what you upload.
No. Check dimensions here, then use Compress to a size if the destination separately limits file size.
What can be opened depends on your browser. JPG, PNG and WebP always work, and a file of another type may need to be saved as one of those in another program first.
The Story preset is 1080 by 1920 pixels, the common portrait story shape. Crop your picture to that shape first so nothing is stretched.