Officially:
Pop Century: 260sq
Port Orleans Riverside: 315sq
Caribbean Beach: 340sq
You'll notice the difference in room size with the space between the foot of the bed and wall as well as the bathroom area. Sometimes its more "wasted" space but I love having a privacy curtain, two sinks, and a fridge. The window makes it feel bigger and adds a little bit more light as well.
I'm not sure you could notice the size difference and walk in saying "omg this is so much bigger" but I definately felt the rooms were more spacious.