Age that ducks stop growing?

[agregg15]

Hi everyone I was planning on ordering duck diapers for my duckling who is about 9 weeks old. Though I have raised ducks from ducklings before I've forgotten when they really stop growing and was wondering when I should measure for the final size. I'm pretty sure she is a Khaki Campbell/Mallard cross and at the moment is completely feathered with adolescent feathers and Mallard sized. Any advice would be appreciated

 

[Amiga]

If I recall, my runners were probably 90% full grown by ten weeks, and then spent another three or four months very slowly filling out. But they had reached pretty close to full grown by sixteen weeks.