A North American standard twin-sized mattress measures 39 inches wide by 75 inches long. A twin-XL mattress, which accommodates taller sleepers, measures 39 inches by 80 inches.
Mattress thickness, or height, varies depending on the amount of padding and other manufacturer specifications. In other countries, standard twin mattress sizes are typically 1 to 6 inches narrower and shorter than the North American mattresses. All mattresses are made slightly smaller to fit inside standard bed frames. Many mattress manufacturers also offer custom-sized alternatives to fit specialty or antique bed frames. Twin-sized mattresses are commonly used in guest rooms, bunk beds, day beds and dormitories or other small spaces.