A trundle bed is a second bed frame that sits on wheels underneath a main bed and rolls out when you need it. During the day it stays hidden. At night, or whenever a guest arrives, you pull it out and you have a second sleeping surface without needing a second bedroom or a spare room full of furniture that sits unused most of the year.
The idea is straightforward but there are a few things worth understanding before you buy one, including the difference between the two main types, what it means for mattress choice, and who it actually works well for.
How a trundle bed works
The trundle sits on a wheeled frame that tucks underneath the main bed. The clearance between the floor and the underside of the main bed frame is what determines whether a trundle fits and how thick the trundle mattress can be. Most trundle frames are designed to accommodate a mattress of around 6 to 8 inches, though this varies by product and is worth checking before you buy.
When you need the trundle, you pull it out by the frame or a built-in handle and it rolls clear of the main bed onto the floor beside it. Most trundles need clear floor space on at least one side of the main bed to roll out fully. This is the measurement most people forget to account for before delivery, and it’s worth sketching out the room before ordering.
The trundle mattress sits at floor level when in use, which is lower than a standard bed. This is fine for most people but worth knowing, especially if you’re setting it up for an older guest or anyone who finds getting up from a low surface difficult.
The two types: roll-out and pop-up
This is the distinction that matters most when you’re choosing between trundle beds, and it’s worth understanding before you commit to one.
Roll-out trundle
The standard type. The trundle frame stays at floor level when pulled out. The sleeping surface is low, roughly 6 to 8 inches off the floor depending on the mattress thickness. It’s simple, reliable, and tends to be more affordable. Most of the daybed with trundle options you’ll find are this type.
The roll-out is the right choice when the trundle is for children or younger guests who don’t mind a low sleeping surface, or when budget is the primary consideration. It’s also the more compact option since it doesn’t need any vertical clearance above it to function.
Pop-up trundle
A pop-up trundle has a lifting mechanism that raises the trundle frame up to the same height as the main bed once it’s pulled out. The two beds sit at the same level and can be pushed together to form one larger sleeping surface, essentially a king size bed made from two twins.
This is the more useful option when the trundle will be used by adults regularly, or when you want the option of combining the two beds for a couple. The sleeping surface at a normal bed height is considerably more comfortable than floor level for most adults. The trade-off is that pop-up trundles are generally more expensive and the lifting mechanism adds mechanical complexity that can wear over time.
Several of the daybed with trundle options in our product list use a pop-up mechanism, which is worth looking for specifically if adult comfort on the trundle is a priority.
| Roll-out trundle | Pop-up trundle | |
| Sleeping height | Floor level (6 to 8 inches) | Same height as main bed |
| Best for | Children, younger guests, budget buyers | Adults, couples, regular use |
| Can beds combine? | No | Yes, forms one large surface |
| Price | More affordable | Higher cost |
| Mechanism complexity | Simple, reliable | More moving parts |
What size mattress does a trundle take?
Most trundles are designed for a twin size mattress, which is 38 inches wide and 75 inches long. The main bed above it is also typically twin size, which means both sleeping surfaces use the same mattress dimensions. This is convenient if you’re buying mattresses for both at the same time.
The thickness of the trundle mattress is more restricted than the main bed. Because the trundle needs to slide under the main frame, there’s a maximum height it can be. Most trundle frames specify a maximum mattress thickness of 6 to 8 inches. Using a mattress thicker than the specified maximum means the trundle won’t slide under the main bed properly.
Check the product listing for the maximum trundle mattress thickness before buying your mattresses separately. It’s one of the more commonly overlooked specs and getting it wrong means returning a mattress, which is considerably less convenient than returning a cushion.
Who a trundle bed actually works well for
A trundle bed makes the most sense when you need occasional sleeping space for a second person but you don’t have a dedicated room for it or you don’t want a second bed taking up space permanently.
Guest rooms are the most obvious use case. A daybed with trundle sits against the wall and functions as a sofa or reading seat when no one’s visiting. When a guest arrives, the trundle pulls out and you have two proper sleeping surfaces ready without moving any other furniture.
Kids’ rooms are the other strong use case. Sleepovers are easier when there’s already a second bed in the room. A trundle under a daybed or a standard bed takes up no floor space during the week and provides a comfortable sleeping surface for a friend staying over at the weekend. For younger children especially, the low height of a roll-out trundle is actually an advantage rather than a limitation.
Small apartments where a permanent second bed isn’t an option but occasional guests are a reality. A daybed with trundle in a studio or one-bedroom apartment means you can host without buying a sofa bed or an air mattress.
Who it works less well for
If the second sleeping surface is going to be used every night by an adult, a roll-out trundle at floor level is not the most comfortable long-term solution. A pop-up trundle addresses this somewhat, but for nightly adult use a proper bed is still the better answer.
If your room doesn’t have clear floor space on at least one side of the main bed, the trundle can’t pull out fully. Before buying a trundle bed, measure the room and work out exactly where the trundle will go when it’s in use. A trundle that can’t be pulled out properly is just dead storage space.
And if the person using the trundle has difficulty getting up from a low surface, a roll-out trundle will be frustrating to use regularly. A pop-up trundle that raises to standard bed height solves this, but it’s worth being honest about the use case before choosing the type.
A quick note on bedding
Standard twin bedding fits both the main bed and the trundle since they use the same mattress size. The only thing to keep in mind is that the trundle mattress is thinner than a standard mattress, so deep-pocket fitted sheets designed for thick mattresses will fit loosely. A regular fitted sheet or one designed for mattresses up to 8 inches works better on a trundle.
We cover this in more detail in our article on whether trundle beds need special bedding, including which sheet depths work best and what to look for when buying bedding for both beds at once.
Trundle bed or bunk bed for a kids’ room?
If the main question is sleeping two children in one room, a trundle bed and a bunk bed both solve the problem but in different ways. A bunk bed gives you two permanent sleeping surfaces stacked vertically. A trundle gives you one permanent surface and one that disappears during the day.
Which one makes more sense depends on whether both children sleep in the room every night or whether the second sleeping surface is for occasional use. We look at this comparison in detail in our article on trundle beds versus bunk beds for kids.
If you want a broader overview of how bed type and size decisions interact with room size and sleeping needs, this bed guide from ArchDaily covers the key considerations worth thinking through before you commit to anything.
If you’ve worked out that a trundle bed is the right direction and you want to look at specific options, our guide to the best daybeds with trundle for small rooms covers the top picks across different styles and budgets with the key specs laid out clearly