How wide the dashboard screen in pixels?

I attended the Smartsheets day, and loved the presentation on creating a better dashboard, however I can't seem to find the image size that will go across the screen. I've created a nice banner image in Powerpoint as suggested, but at best it works 3/4 screen at about 8 squares wide with a white border.

Alternately, what is the pixel size of just one design square on the dashboard?