How to get Gridview width

I have a Gridview1 linked with sqldatasource so it is a standard type.

Its width changes according to the data each time, so it is auto width adjusted.
There is a Label1 on the page too. I have also a button on the page. I want to click the button and get the Width into Label1.
This means when the user click the button, the Gridview1 already has the width.
I need to get the width of this Gridview each time to a label to display on page.
What is the code ?
Thanks