According to online retailers, a standard twin-sized mattress from most manufacturers typically measures 75 inches in length and 39 inches in width. Commonly referred to as a "single," such mattresses are generally meant to accommodate one child or adult.
Standard American mattress sizes increase to the twin XL, which bears the same width but has 5 additional inches of length, and the full-sized mattress, which measures 54 inches wide by 75 inches long. Queen size (60 inches wide by 80 inches long) and king size (76 inches wide by 80 inches long) are the recommended sizes for comfortably accommodating two adults. Some mattresses are also offered in California king size, which measures approximately 72 inches wide by 84 inches long.