Trundle Bed Size & Dimensions Guide

Trundle bed sizes can be confusing. This article will explain everything you need to know, from mattress size to height off the floor.

We’ve also written in-depth articles on the best trundle beds (here) as well as trundle mattresses (here).

Trundle Bed Dimensions

Trundle bed size: 75″ x 38″

A trundle bed refers to the lower bed frame that slides under another bed but can sometimes be used to describe the two together, as a set.

The lower “trundle” is usually a standard twin size bed to allow for a regular twin mattress to fit perfectly.


The “upper” bed is usually a twin or daybed but can also be a double or queen. The frame is about 2 inches larger all-round to accommodate the trundle underneath.

Whenever possible, you should always buy the set as some trundles won’t fit under a regular bed.

Trundle Bed Height

Trundle Bed Height: 12 Inches

We usually refer to the height as the space between the upper sleeping area and the floor. In other words, “how much space is there to fit a trundle under the bed”.


The 12 inches of space is usually taken up by the 4 inch trundle frame allowing another 8 inches of mattress space. If you’ll be using the trundle regularly, you should consider leaving some room for bedding as well by either choosing a 5 or 6 inch mattress.

Is a Trundle Bed Smaller Than a Twin?

No. It’s exactly the same size to allow a twin mattress to fit. (75″ x 38″)

It’s the upper frame that’s slightly larger to accommodate the trundle.

What Size Mattress Fits a Trundle Bed?

A standard twin (75″ x 38″) will fit perfectly in almost every case.

Manufacturers know that mattresses come in standard sizes and have to build the trundle frames accordingly.

Take note of the height though!

Not every mattress will fit under the upper frame. The limit for mattress height (thickness) is usually around 8 inches. Consider leaving some room for a comforter too.

Another important consideration is to try and match the top mattress with the trundle one. It makes it easier to swop the around after some regular use.

If you have a pop-up trundle bed, (which raises up to meet the top bed) having both mattresses line up is essential to create the effect of a double bed.

Will a Trundle Fit Under Any Bed?

No! Most bed frames don’t have the extra sliding room to accommodate a regular sized twin trundle. (Some even have a leg in the middle making it altogether impossible.)

If you’re buying the trundle separately, it will most likely be slightly smaller than a twin to allow it to fit (retrospectively) under a regular twin bed. However, this will still not make the regular twin mattress fit!

This is why it highly important to buy the two as one set if possible.

If you do buy a separate trundle, you’ll most likely be frustrated every time you want to move the trundle in our out from under your bed.

The best way to test is to take your existing twin mattress off your bed and try to slide it along the floor under your bed. This will give you some idea of what it will be like if you bought the extra trundle separately.

Various Trundle Bed Sizes

Trundle beds come in all shapes and sizes. The trundle itself is usually twin (a.k.a. single bed) but the upper part of the bed can be anything from a twin daybed to a double bunk bed!

Here are some examples: