Double mattresses are the most common mattress sizes in the UK, with many couples opting for this mattress size. The dimensions of 135cm x 190cm or 4’6x6’3 means that this mattress size is spacious enough to fit two sleepers. It also allows single sleepers to fully stretch out. Double size mattresses can fit in most standard bedrooms, without taking up too much space. So, it’s a great option for master bedrooms.