How are area rugs sized? Can I trust the dimensions quoted?

I was looking at a web site that sells rugs online and ships to you. There are some nice rugs at pretty good prices.

My question is this: How accurate is the sizing for area rugs? If I see at 8×10 foot rug, for example, is it really 8 feet wide? Or is it 7’9” or something similar?

I know that when it comes to lumber, a 2×4 is really 1.5“x3.5”. Are rugs the same? Do they cheat on the dimensions?