by Quick answer: A twin mattress is 38 by 75 inches — best for children, single sleepers, bunk beds, and small rooms. A full is 54 by 75 inches — 16 inches wider, ideal for a solo adult who wants more room or a snug fit for two. Both are the same length.
By the MattressNut editorial team · Updated June 2026
Twin vs Full — The Short Answer
The only difference is width: a twin is 38 inches wide, a full is 54 inches. Both are 75 inches long. Choose a twin for kids, guests, bunk beds, or tight spaces. Choose a full for a single adult who wants to spread out, or as a tight squeeze for two people in a small room.
How They Compare
| Step / Factor | Detail |
|---|---|
| Dimensions | Twin: 38" x 75". Full (double): 54" x 75". Same length, full is 16 inches wider. |
| Best for a twin | Kids and teens, single adults in small rooms, bunk beds, daybeds, and guest rooms. |
| Best for a full | A solo adult who wants more sprawl room, or two people willing to share snugly (each gets ~27"). |
| Room and budget | Twins cost less, fit smaller rooms, and use cheaper bedding. Fulls need more floor space but suit adults better. |
Practical Tips
For a growing child or teen, a full can last into adulthood and saves buying a bigger bed later. For two adults sharing nightly, a full is tight — a queen (60" wide) is usually the more comfortable step up. Measure your room and leave walking space on at least one side before deciding.
Our Recommendation
Pick the size by who sleeps on it and how much room you have: twin for kids and single sleepers in tight spaces, full for an adult who wants more room. Once you've settled on size, comfort and support matter just as much. The Saatva Classic comes in both twin and full, in three firmness options, with a 365-night home trial to confirm the feel is right.
See the Saatva Classic and its 365-night trial
The Bottom Line
Twin (38x75) suits kids, single sleepers, and small rooms; full (54x75) gives a solo adult more space or fits two snugly. Same length — it comes down to width, room size, and who's sleeping.
Bottom line: Choose a twin for kids and tight spaces, a full for a solo adult who wants room or a snug two-person fit.
Related: our full Saatva mattress review.