If you are wondering which size for a watermark is the best, you should know, the size of the watermark depends on the size of the image.

Example: If the watermark is 512x512 and image 1024x1024, the watermark will take up half the image.

Suggestion:

We recommend the following watermark sizes depending on the size of the image

Small

watermark_small_64px 

Medium

watermark_medium_128px  

Large

watermark_large_256px, watermark_extra_large_512px 

Find out more about watermarks here: https://www.youtube.com/watch?v=D9SIvOixZ5U