Trundle Bed Dimensions and Fit Check
Pick a trundle size, then enter the clearance under your bed, the mattress thickness and the floor beside the bed to see what fits.
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How to use the Trundle Bed Dimensions Tool
- Choose a Trundle mattress size: Twin, Twin XL or Full. The tool starts on Twin.
- Read the three headline results: the mattress size, the mattress thickness that fits, and the floor space needed beside the bed.
- To get your own thickness limit, measure from the top of the trundle deck to the bottom edge of the main bed’s frame, then type it into Clearance under the main bed (optional).
- Type the Mattress thickness (optional) of the one you are considering. The “Thickness check” row says whether it fits.
- Open More options to type the Floor space beside the bed (optional), measured from the side of the main bed to the nearest wall or furniture. The “Floor space check” row compares it with what the trundle needs.
- Choose your Units, inches or centimeters. Measurements you type are converted for you.
- Scroll down to the size table, the thickness table and the legend of guides B, P and M.
The preset buttons fill in common cases: “Twin trundle”, “Twin XL, 60 in of floor”, “8 in clearance, 8 in mattress” and “Full trundle”. If a field you typed is zero or not a number, the tool shows an error.
What size is a trundle bed?
A trundle bed takes a twin mattress in most cases. Three guides give the same figures: twin 38 by 75 inches and twin XL 38 by 80 inches. A full trundle (54 by 75 inches, 16 inches wider) exists on some larger frames, but one guide calls it less common and one bed maker does not build full or queen trundles at all, because they exceed the usual clearance under a bed.
| Size | Width × length | Centimeters | Floor space needed |
|---|---|---|---|
| Twin | 38 × 75 in | 96.5 × 190.5 | 62–74 in |
| Twin XL | 38 × 80 in | 96.5 × 203.2 | 62–74 in |
| Full | 54 × 75 in | 137.2 × 190.5 | 78–90 in |
Is a trundle mattress the same size as a twin?
Yes in width and length, no in thickness. A trundle mattress is typically 6 to 8 inches thick. A standard twin is 10 inches or more, and standard mattresses in general run 10 to 14 inches. A mattress that thick will not slide under the main frame.
How thick a mattress fits under your bed?
Measure the clearance, then subtract half an inch.
Largest mattress thickness = clearance − 0.5 in
For example, 8 in between the trundle deck and the bottom of the frame gives 7.5 in (19.1 cm), so a 7-inch mattress fits and an 8-inch one does not. One bed maker advises mattresses up to 6 inches for most trundles, and says models with extra clearance may take 7 or 8. It also notes that enclosed (“boxy”) trundles need a slimmer foam mattress, while open slatted ones take foam or hybrid. Pop-up trundles that rise to bed height can take thicker mattresses once raised, but the mattress still has to fit underneath when stored.
How much floor space does a trundle need?
A trundle rolls out sideways, so it reaches about its own width past the side of the main bed: 38 inches for a twin. A bed maker advises leaving at least 2 to 3 feet free once it is fully extended, so you can climb in. Floor space needed is the width plus 24 to 36 inches: 38 + 24 = 62 in at the least and 38 + 36 = 74 in for a comfortable fit. A full trundle needs 78 to 90 inches. The reach is our own geometry, not a number the guides publish.
Sources (checked 24 October 2026): bunkbedscanada.com · puffy.com · mattressmiracle.ca
Worked examples
| Input | Result |
|---|---|
| Twin trundle | floor 62–74 in, thickness 6–8 in |
| Twin trundle | floor 62–74 in, thickness 7.5 in |
| Twin XL trundle | floor 62–74 in, thickness 6–8 in |
| Full trundle | floor 78–90 in, thickness 6–8 in |
| Twin trundle | floor 62–74 in, thickness 9 in |
Calculated by the tool above; open it with the same values to see each step.
How this tool works and where the numbers come from
Mattress sizes and the 6 to 8 in thickness range are the figures three trundle guides publish, shown source by source, not averaged. The largest thickness is your measured clearance minus half an inch of wiggle room, the rule one mattress retailer gives. Floor space is the trundle width plus the 2 to 3 ft of free space one bed maker advises beside an extended trundle. Reach is our own geometry (a trundle rolls out sideways, about its own width), not a published figure.
Sources
Frequently asked questions
What is the standard size of a trundle bed?
Twin: 38 by 75 inches (96.5 by 190.5 cm) for the mattress. Twin XL, at 38 by 80 inches, is the other common size.
Can an adult sleep on a trundle bed?
Guides suggest a twin XL trundle for teens and adult guests, and a 7 or 8 inch hybrid or innerspring mattress for better comfort if the clearance allows. Check the weight limit in the frame’s spec sheet; the guides here do not give one.
Will a regular twin mattress fit a trundle?
Only if it is thin enough. The width and length match, but a 10 inch mattress is thicker than the 6 to 8 inches most trundles take. Use the clearance field to find your limit.
Why do the thickness figures differ between guides?
One guide says up to 6 inches, two say 6 to 8, and the real limit is your frame. The tool shows the 6 to 8 inch range when you leave the clearance blank, and your own measurement when you type it.
Do boxy and open trundles take the same mattress?
Not always. Enclosed trundles have lower inner clearance and suit slim foam mattresses; open slatted trundles are more forgiving, so measure inside the deck before ordering.
Related tools
- Bunk Bed Dimensions: Use this when the trundle goes with a bunk bed.
- Dresser Dimensions and Fit Calculator: Use this to check a dresser still fits once the trundle is out.
- Bed Height: Use this to check how high the main bed sits from the floor.
- Rug Size for a Queen Bed: Use this to choose a rug that fits beside a queen bed.
- Bedroom Area Rug Size: Use this to pick a rug for a bedroom with a bed and a pull-out.
- Nightstand Height: Use this to match a nightstand’s height to your mattress top.