What size should my logo be to use as a watermark on my posts?
If you want to upload your logo to use as a watermark on your posts, it must be a maximum of 2000 pixels, in both horizontal and vertical dimensions. So neither the height nor width can exceed this amount.
The Padding % and Width % options in the "Watermark" section when adding or editing a post allow you to place your logo how to desire on your posts.
Each image file can be up to 200MB, so you don’t need to worry about the size of the file.
When it’s uploaded to your Media Library, your logo will be resized and optimized to use as your watermark.
It can be uploaded as a JPG, but PNG files work best.