Photo posts are shown full-screen. A 9:16 image fills it; a 4:5 or square photo is shown with background bars. Captions, the sound bar and the buttons cover the bottom and the right edge, so keep text out of the lower 20% and away from the right side.
TikTok limits photo posts to 1080p, so a 1080×1920 export is the maximum useful size. Larger uploads are scaled down and compressed.
Try it on your own photoDrop a photo at the top of the page. Ten seconds later it's sized, sharpened and ready to post.
Compress a photo