What Size Mattress for a Trundle Bed? Your Clear Guide to Getting It Right
If you’re asking “What size mattress for a trundle bed?”, you’re usually trying to avoid a frustrating mismatch: a mattress that’s too thick to slide under, or too long or wide for the frame. This FAQ-style guide walks through the most common trundle sizes, how to measure, and what else to consider before you buy.
What Size Mattress Does a Trundle Bed Usually Take?
Most trundle beds are designed for a twin or twin XL mattress, but there is no single universal standard. The upper bed might be one size and the pull-out trundle another.
Common trundle mattress sizes include:
- Twin trundle – about 38" x 75"
- Twin XL trundle – about 38" x 80"
- Full trundle – about 54" x 75" (less common)
- Custom/specialty trundle – varies by manufacturer
The thickness is just as important as length and width. Many trundle frames only fit a mattress that is 6–8 inches high, sometimes less.
Why Does Trundle Mattress Size and Height Matter?
Choosing the right size mattress for a trundle bed affects:
- Fit and function – A mattress that’s too tall may prevent the trundle from sliding fully under the main bed.
- Comfort – Very thin mattresses can feel firm or use less cushioning than a regular bed.
- Safety and appearance – An overstuffed trundle can put strain on the frame or look uneven when pushed in.
Always check the trundle’s internal measurements before deciding what size mattress for a trundle bed will work best.
How Do I Measure My Trundle Bed for the Right Mattress?
To figure out what size mattress for a trundle bed you specifically own, use a tape measure and check three key dimensions inside the pull-out frame:
- Length: Measure the inside from head to foot.
- Width: Measure side to side between the rails.
- Height clearance: Measure from the base (slats/platform) up to the bottom of the upper bed frame or any crossbars.
Then compare those numbers to standard mattress dimensions.
Simple Trundle Mattress Fit Guide
| Feature | What to Check | Typical Range |
|---|---|---|
| Length | Inside frame head-to-foot | 75" (twin), 80" (twin XL) |
| Width | Inside rail-to-rail | 38" (twin), 54" (full) |
| Maximum height | Floor to underside of top bed frame | Often 6"–8" |
| Extra clearance | Small gap so the trundle slides easily | Around 0.5"–1" |
If your measurements are slightly smaller than a standard mattress size, you may need a thinner or slightly narrower style, or a custom option.
How Thick Should a Trundle Mattress Be?
For most frames, a trundle mattress should be no more than 6–8 inches thick. Some very low-clearance styles may require 5 inches or less.
A few practical tips:
- Check the manual or label on your trundle frame if you still have it; it often lists a maximum mattress height.
- Account for bedding – a thick mattress plus a bulky mattress protector may reduce clearance.
- Prioritize support – many people choose a firmer or more supportive mattress if it’s on the thinner side.
Can a Trundle Bed Use a Different Size Mattress Than the Top Bed?
Yes. The top mattress and the trundle mattress do not have to match in size.
Common setups include:
- Twin over twin trundle – most typical for kids’ rooms and guest spaces.
- Twin over full trundle – twin on top, full-size pull-out below (or vice versa).
- Full over twin trundle – full-size upper bed with a twin trundle underneath.
What matters is that the trundle mattress fits the lower frame exactly and slides in and out smoothly, even if the upper bed is a different size.
What Type of Mattress Works Best on a Trundle?
While the main question is what size mattress for a trundle bed, many people also wonder about mattress type. In general:
- Foam or hybrid mattresses often work well because they’re available in thinner profiles and handle lower clearances better.
- Very tall, traditional innerspring mattresses may be too thick for many trundles.
- A lightweight mattress can make pulling out and pushing in the trundle easier.
As long as the mattress is the right size and thickness, the specific type is usually a matter of comfort preference.
✔️ Quick Mattress Takeaways
Key points to understand about what size mattress for a trundle bed
- Most trundles are designed for a twin or twin XL mattress, with full-size options less common.
- Measure your trundle’s interior length, width, and height before buying a mattress.
- Typical maximum trundle mattress height is around 6–8 inches; some need less.
- The top and bottom mattresses don’t have to be the same size; only the trundle frame’s measurements matter.
- Leave a bit of extra clearance so the trundle can slide in easily, even with bedding.
- Consider a thinner, supportive mattress style to balance comfort with the low profile many trundles require.
Choosing the correct size mattress for a trundle bed comes down to careful measuring and paying close attention to thickness. Once you know your frame’s exact dimensions and height limit, it becomes much simpler to select a mattress that fits smoothly, feels comfortable, and keeps the trundle working the way it should.
