Zoella's bra size is a 34b, although she admitted to me that it fluctuates and goes up and down depending on her weight.
Se also had weight issues when she was younger, and was even scared that her hips and boobs would never grow.
Goes to show that all of us have confidence issues at some point!
Want to read about her weight issues and lack of confidence? Here's the blog post she mentions about it (she also talks about boobies!)
http://www.zoella.co.uk/2011/03/why-are-you-so-skinny.html