TikTok profile picture size
Cropped in your browser · your image is never uploaded
TikTok asks for at least 200 × 200; upload 400 × 400 so it stays sharp. In the feed it appears at roughly 48 pixels with a follow button overlapping the bottom.
How to use the tiktok profile picture size
The follow button is the TikTok-specific detail. In the feed your avatar sits in the right-hand column of buttons with a red plus overlapping its lower edge, so anything positioned at the bottom of the circle is partly covered. Combined with the 48-pixel display size, that means the only thing that works is a centred face or a single bold shape. TikTok also allows a profile video rather than a still, which loops on your profile page but still falls back to the still image everywhere else, so the still is what actually matters.
Questions
At least 200 × 200. Upload 400 × 400 for a sharper result.
Around 48 pixels, with the follow button overlapping the bottom.
Yes, on your profile page. Everywhere else falls back to the still image.
Yes, from your square upload.
Between the 48-pixel size and the follow button over the bottom, only a centred face or bold shape survives.