What are the differences in size between Twin, Twin XL, Full, Queen, King, and Cal King mattresses? How many people are recommended to sleep on each size?

Twin mattresses (38" x 75") are typically only suitable for one person.
Twin XL mattresses (38" x 80") are slightly longer than Twin mattresses and are a good option for taller people.
Full mattresses (54" x 75") are larger than Twin mattresses and can accommodate two people tightly.
Queen mattresses (60" x 80") are the most popular size for couples and offer enough space for two people to sleep comfortably.
King mattresses (76" x 80") are ideal for two people wanting extra space to spread out.
Cal King mattresses (72" x 84") are slightly longer than King mattresses and are a good option for taller two people.