max header height and width?

on the box view on Leaf theme, what is the height and width of the header from end to end and from top to the top of the menu?

im in the process of creating a new header with image and text..

on my site you can see that my current header starts aligned on the left side but on the right side it goes slighlty past the border.
Likewise, I want my image to meet the border of the main menu so there is no gap in between like there is currently.

Is there an easy way to figure this out? Or does anyone know the size available there?

Thanks for the help!