Hello Nguyen,

If I am not mistaken, there is no method to resize its width.
However, I think you still can use width and height with 100% value.
Please place WebGrid inside a div container.
When you resize the popup, you only need to change the div height/width style.
WebGrid would follow the div because both the width and height are set 100% which would follow the div.
One thing you would need to pay attention, please do not resize the width/height to very small amount because the status bar and footer would hardly show.

Regards,
Handy

I made a simple test of WebGrid based on your information. In my test page, I uses AutoHeight and AutoWidth feature of WebGrid in order to have WebGrid resize correlative with the windows width. AutoHeight and AutoWidth property specifies whether WebGrid will calculate its height and width automatically based on available page’s height.

I enclosed my test page as attachment. for more detail information, please check my simple test page and let us know whether it helps or not.