The diamond is 4.8 [something], and you can add [carats] or [millimeters], depending on what characteristic you want to describe for the diamond, it's carat weight or its round brilliant cut diameter, respectively.
The Diamond as Big as the Ritz was created in 1922.
48
You can browse the Tiffany site, below (without endorsement), to find the 48 carat diamond that you want to purchase from them. Otherwise a 48 carat diamond is a large diamond and may only be available from an auction house if you cannot find one at Tiffany's.
level 48
lv 48 in Diamond and Pearl
gabite evolves at lvl 48
If the diamond is an ideal emerald cut with these measurements, the diamond may weigh about one quarter of a carat. Otherwise, you have stated the diamond's 'big' size in measurements.
Gabite evolves at level 48
You've given the carat weight of a diamond. 'Big', then, is based on the cut of the stone.
48 inches = 4 feet = 1.2192 meters
The Sahara Desert is nearly as big as the contiguous 48 states.
it evolves into gabite at 24 and garchomp at 48