A queen-size mattress measures 60 inches wide by 80 inches long. A California king mattress measures 72 inches wide by 84 inches long. An Eastern king mattress measures 76 inches wise by 80 inches long.
Both queen- and king-size mattresses can accommodate two sleeping adults; however, a king-size mattress will probably be more comfortable as long as your room is large enough to hold one.
There should be room to walk around on either side and in front of the mattress. If you will not have at least 2 feet of clearance around a king-size mattress, a queen-size mattress will probably be better-suited to your room.
In addition to measuring your room to see if your mattress will fit, always measure the spaces the mattress will need to fit through to get to your room.
It is hard to discern the difference between a California and eastern king mattress by just looking. Always measure your mattress before purchasing a bed frame.