King Single Mattress Size: 2030 x 1070mm. This size is ideal for, kids, teenagers and adults. King Single mattresses are mainly advised for those growing teenagers who are too tall for single mattresses. King Single mattresses are wide than single mattress by approximately 15cm or 6 inchs. It gives your child or yourself that extra room compared to a single mattress. We recommend king single mattress for those teenagers that have had a growth spurt and single mattresses just aren’t long enough for them.