Can you fit another chair next to the couch? No matter how good one is at looking at space, there are always moments when eying something doesn't quite cut it. That is why we tape out furniture shapes (and sizes) on the floor of a room before plopping down the cash for the big-ticket items.
Another great solution is the Icovia website program, which allows you to easily select, arrange and rearrange furniture to the exact measurements of your space. The program ain't cheap ($29.95/month) but there is a free sample, and in truth, the $30 just might be worth it before you blow $2500 on that 92" sofa for the den.