Cal King vs King
What is the Difference Between a Cal King and King?
King (can also be referred to as an 'Eastern King') is 76" wide x 80" long
The King is the widest bed commonly available. Its 4" wider than the Cal King. Its length of 80" is sufficient for most people. Potential drawbacks include the width of the bed not fitting into smaller rooms.
California King (usually called 'Cal King') is 72" wide x 84" long
The Cal King is the longest bed commonly available at 84". Potential drawbacks include the bed not being wide enough for 2 adults or the length not fitting easily into the room.
What one to pick? Simple, if you want more width than length go with the King. If you want more length than width, go with the Cal King.
Additional Reading: What's The Right Size Bed Right for You?