Which length do you determine for a mantel shelve? We are redoing our fireplace and we don't know what device...

We are redoing our fireplace and we don't know what device to go by. The marble is 60" inches across, so thats how long we want the bottom of the mantel shelve to be. We are looking at both custom and premade mantels. For the custom ones, the website clearly shows which calculate is which, but for the premade ones it doesn't show.

this is one of the mantles we are looking at and we don't know if it is the right length.

http://www.lowes.com/lowes/lkn?action=pr...

it say its 5 feet so is that only just right, or that the length on top?
much appreciated
Answers:    I would assume that is at the longest point, but you could ring Lowes and they will tell you.