What Is a Twin Mattress? | The Standard Small Bed Size

A twin mattress measures 38 inches wide by 75 inches long, making it the smallest standard adult mattress size in the United States.

If you’re shopping for a bed for a child, a guest room, or a small apartment, the twin is likely the size you need. It fits one sleeper comfortably and leaves extra floor space, which is why it’s the go-to for bunk beds and compact bedrooms. The twin XL, a close relative, adds five inches of length for taller sleepers. Understanding exactly how a twin mattress measures up—and whether it’s right for your space—comes down to a few straightforward facts.

Twin Mattress Dimensions: The Exact Numbers

The standard US twin mattress is exactly 38 inches wide and 75 inches long. That’s roughly 3 feet 2 inches by 6 feet 3 inches. This size is designed for one person and is the narrowest and shortest of the common adult mattress sizes.

Here’s the quick breakdown of the two twin variants you’ll see in stores:

Keep in mind that a small number of brands may differ slightly in actual dimensions, but 38″ × 75″ is the industry standard for a twin in the US, as confirmed by the Sleep Foundation’s twin mattress size guide.

Who Is a Twin Mattress Actually For?

Because of its compact footprint, the twin mattress serves a very specific set of situations. It’s the standard choice for kids and teens moving out of a crib, and it’s also a smart fit for single adults in small apartments where floor space is at a premium.

You’ll most often see twin mattresses in these settings:

• Children’s rooms — enough space for a growing child, with room left over for toys and a desk.
• Guest rooms — a twin keeps a spare room from feeling cramped while still offering a proper bed.
• Bunk beds — the standard size for stacked beds because of its lighter weight and narrower width.
• Dorm rooms — though these usually require a twin XL, which you’ll read about below.

A twin is generally not recommended for two people, even a couple. At 38 inches wide, it’s noticeably narrower than a full-size mattress, so most adults will find it too snug to share comfortably. If you’re furnishing a room for two or need extra space for a pet, you’ll want to size up.

What’s the Difference Between Twin and Twin XL?

The twin XL is identical in width—38 inches—but measures 80 inches long instead of 75. That extra five inches makes a meaningful difference for anyone over 6 feet tall, who might otherwise find their feet hanging off the end of a standard twin.

You’ll find twin XLs most commonly in college dormitories, since they accommodate a wider range of student heights while still fitting into compact rooms. The trade-off is that twin XL sheets and mattresses are less common in standard retail stores, and the price can be slightly higher. For a child or a shorter adult, a standard twin is generally the more practical and budget-friendly choice. Just be sure to check whether the bed frame you’re buying fits a 75-inch or an 80-inch mattress, as the two are not interchangeable.

Twin vs. Single: Is There a Real Difference?

No—in the United States, “twin” and “single” refer to the exact same mattress size. The two terms have been used interchangeably for decades, and both describe a 38-inch wide by 75-inch long mattress. Most manufacturers and retailers today list it simply as “twin,” but if you see “single” on an older product listing or in a furniture store, you’re looking at the same dimensions.

One detail worth checking when you buy: a twin frame and a twin XL frame are not compatible, so always confirm the length before purchasing a base or headboard. If you’re a taller teen or an adult over 5’10”, the twin XL is worth the extra cost. For everyone else, the standard twin will serve you well for years.

When you’re ready to pick one, our roundup of the best twin bed mattresses can help narrow down the options quickly.