There is a standard sizing for mattresses throughout the industrie Twin, Twin long, Full, Full Long, Queen, Cal King, King. in that order, yes a King is bigger than a Cal King. Whats best for you? Think about how you sleep and who sleeps with you, Wife, Husband, Pets, and base your descision on that. you also want to take into consideration how you sleep. If you are the type of person that likes to cuddle well a queen might be the right size as if you want your roll around room perhaps a king size will be a better option. If your a college student just grab a twin or a full.
Twin size is made to accommodate one child or one adult sleeper. When you need to lay with your child it should accommodate, but will be a bit crowded. If you are a taller adult you may want to consider a twin-XL which will give you added length. (see below). Twin (also referred to as ‘single’) is great for smaller guest spaces, bunk beds, etc.
Twin-XL size (Extra-Long) is 5 inches in length longer than the standard twin. This size is great for taller youth or adults. Basketball players listen up. Twin-XL is the same length as a queen or king, In fact two of them side by side equals a king.
Full size or also known as a ‘double' was commonly used for two adults 30 - 40 years ago when the homes and bedrooms were built much smaller. Now it is usually purchased for single person use and sometimes smaller guest rooms. It is a tight fit for two adults and the same length as a twin. Two adults sleeping on a full size is equivalent to each person sleeping on a crib mattress (27 inches of sleep space). Most people with a sleeping partner opt for the queen size. Full can sometimes be special ordered in extra long. This would be an option for the cuddler. =)
Queen 60''x 80'' (inches)
Queen size is the most popular size sold. Ideal for two adults who don't want a king size in order to save living space. Also great for those who just like to spread out.
King size (also known as an eastern king) is the same length as a queen but much wider (16 inches). If you have the space it offers the most room for couples. King size beds are also great if you have kids or pets who like to share your bed. For very tall people you can also special order a California-King which is a 72'' x 84'' but trying to find sheets for this size is a nightmare and a headboard setup is also really hard to find.
Hope this helps !