Is there a standard size for the width of a website in a mockup? What is that size? Why?
I start most of my mockups at 1200px wide even though I'm designing for 1024px resolution. I set up guides within the mockup for 1000px. The height may vary. The reason I make my mockup file wider is to see how the design feels with breathing room around it. Most people use higher than 1024px these days.