In addition to what Meg said......if you look at the Royal Caribbean website, and look at the various cabin descriptions, you will see the sizes of the cabins. For example, a D1 is 178 sq. ft., a Grand Suite is 358 to 384 sq. ft., etc. The website also describes the amenites of the various cabins.
We sailed Serenade from San Diego to Hawaii and back in 2007. It was great! We also had a D1 cabin on that sailing - 9256, which is an aft cabin. The cabin was the same size as other D1's, but the balcony is larger. Enjoy!
Serenade of the Seas b2b January 2016
Serenade of the Seas b2b January 2017
Sailed the Serenade twice both time in the Jr. Suite. They are very spacious. I think they are about 279 sq. ft. plus a nice size balcony. It is always enough room for DW and I. Nice size bathroom with tub and shower and a walk-in closet. There is also a sitting area in the Jr. Suite. Really nice.