What Size Is A Bunk Bed Mattress?

February 18, 2021 | Casper Editorial Team

Bunk beds are the perfect solution for kid and adult problems alike — parents save space while children enjoy the fun of an elevated bed. Plus, who doesn’t love a never-ending sleepover? 

The bunk bed, however, is only one part of the equation. The mattress is the other component.

So, what size is a bunk bed mattress? Put simply, it depends on the bed. 

Our innovative twin size mattresses are made from multiple layers of cooling foam. Then they’re squeezed down into a tiny box, which magically appears on your doorstep within a few days.

Different Types of Bunk Beds

Bunk beds are generally designed for children, so the range of bunk mattress sizes is limited to the smaller end of the spectrum. Most bunk beds use twin mattresses, but they’re not the only kind available:

  • Two twins – A standard bunk bed will fit two twin mattresses, each measuring 38 inches wide and 75 inches long.
  • Two twin XLs – Some bunk beds are specifically designed to fit twin XL mattresses, which have the same width as a standard twin mattress but five additional inches of length — 38 inches by 80 inches — making them as long as a king or queen size bed. When comparing a twin vs twin xl mattress, twin xl mattresses are usually the better option for taller people.
  • Two fulls – Full size bunk beds are less popular than the other two, but are becoming increasingly common for teenagers and even college students sharing a room. Full mattresses measure 53 inches by 75 inches. If you compare a full vs twin, they’re the same length but a full has an extra 15 inches of room side-to-side.
  • One twin, one full – This is another fairly common configuration, especially for children of various ages sharing a room. The upper bunk is a twin, while the lower bunk is a full. This gives more room to the sleeper below (or some extra space for parents to cuddle up next to their kiddo for a bedtime story).

There are also loft beds that have open space underneath for a desk, futon, or storage area. The top is essentially the same as the top of a bunk bed, with a twin, twin XL, or full mattress. 

If you’re not sure of your bunk bed’s size, measure the inside dimensions before you start mattress shopping. Buying the wrong size could actually be a safety concern if it hangs over the guard rail.

Choosing the Right Bunk Bed Mattress

What kind of mattress for bunk beds is best? 

Bunk bed safety and sleep quality are important considerations to account for when making your choice of mattress. 

To that end, consider a mattress that is:

Low Profile 

The ideal thickness for a bunk bed mattress, specifically for the upper bunk, is about six or seven inches. A low mattress height will maximize the efficacy of the safety rail and increase the available headroom, while still being thick enough to provide comfort and support. Naturally, if your bed has higher guard rails, you can enjoy a thicker mattress.

Quiet Model

Sharing a bunk bed can be tricky, especially if the top sleeper is a tosser and turner on a creaky mattress. Again, for the top bunk especially, consider an all-foam mattress to reduce nighttime disturbances. 


A thick, heavy mattress on the top bunk will pose a safety risk to both children. Always check the listed maximum weight capacity for your particular bunk bed — then find a thin, light mattress to match.

Temperature Control

Hot air rises, meaning the top bunk will always be a few degrees hotter on those warm summer nights. If you can find bunk bed mattresses with cooling technology, you’ll be able to ensure a comfortable night’s sleep for both people, no matter the weather.

For many families, bunk beds are temporary. Your kids may grow out of a bunk bed mattress, however, it’s best to spend a little extra now for a durable, comfortable mattress so you can get the most out of it. You can always repurpose the mattresses into a larger bed after your children outgrow their bunk beds by pushing them together. If you’re wondering what size two twin beds make, it’s about the size of a king mattress.

Equipping Your Bunk Beds with Casper Mattresses

Casper mattresses come in the three most popular bunk bed sizes: twin, twin XL, and full (as well as queen, king, and California king for any non-bunk beds). Between our four unique mattress types, you’ll be able to find something for both top and bottom bunks, including:

  • All-foam or hybrid compositions for a creak-free sleeping experience
  • Several varied layers for a uniquely comfortable feel
  • Perforated, breathable foam for advanced cooling technology
  • A durable base layer across all mattress models, plus additional foam, plush top layers, gel pods, and ergonomic zones for increased support 

From the Element — our simplest, thinnest design — to the Wave and Wave Hybrid — our most advanced support system — Casper has deluxe mattresses to fit any type of bed. 

We know kids can be picky, so try a Casper twin size mattress for 100 nights, risk-free. Soon enough, they’ll be telling you that it’s bedtime.