I'm trying to get the width of a div so that I can echo it out in php. 

Can anyone give me a pointer as how to achieve this? 

Basically, I'm wanting to develop a 'responsive' `<div>` which will display the width of the parent `<div>` in php in a responsive template. Obviously, in different window sizes, the responsive template changes width size and I just need to find a way to output this width and echo it out in php. JQuery is already running in the background, so I could tap into that... 

Just need a bit of direction