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A trundle is one of the highest-value builds for a small bedroom: a shallow rolling box that tucks under an existing bed and pulls out as a second sleeping surface or a huge storage drawer. It's mostly a plywood bottom framed with tall side boards, and the engineering trick is in the casters.
Everything is custom to your bed, so measure first: the critical number is the clearance under your bed. This design uses 1x8 sides and needs at least 8" of clearance; with more room you can step up to 1x10 for a deeper box. The plywood bottom is cut to your under-bed footprint — the source example cuts a 72" length down to 70-1/2" and keeps the 38-1/2" width — so a full run of the bed frame length minus a bit for clearance.
About sag: a wide, shallow plywood bottom would bow in the middle under a mattress and a sleeper, and the fix isn't a thicker bottom — it's wheels. Put a caster at each of the four corners and two more in the center of the span, so the floor supports the middle directly. Six low-profile casters (at least 2-1/2" overall) keep it rolling and keep it flat. Finish it so it slides on your floor without scuffing.
| Item | Qty |
|---|---|
| 3/4" plywood or MDF, 4x8 sheetThe bottom platform. | 1 each |
| 1x8 or 1x10 board, 8 ftSides — 1x8 for 8" clearance, 1x10 if you have more room. | 3 each |
| Caster wheels, 2-1/2"+ overallFour corners plus two in the center to stop the middle sagging. | 6 each |
| Wood screws, 2" | 40 each |
| Wood glue | 4 oz |
| Wood putty | 4 oz |
| Finish | 12 oz |
Overall cost: $$. Lumber prices vary by region, species, and season, so we give a band rather than a figure we would only be pretending to know.
| Part | Qty | T × W × L |
|---|---|---|
| Bottom platform3/4" plywoodCut to your under-bed footprint — width = C, length = bed length minus ~1-1/2". Example shown. | 1 | 3/4" × 38 1/2" × 70 1/2" |
| Long sides1x81x10 (9.25" wide) if you have more clearance. | 2 | 3/4" × 7 1/4" × 70 1/2" |
| End sides1x8 | 2 | 3/4" × 7 1/4" × 38 1/2" |
Buy 4 boards at 8 ft.
1 board
3 boards
Assumes 8 ft stock, a 1/8" saw kerf, and buying each part at its own width. Change the board size or kerf on the full board plan →
Measure the clearance under the bed first — this design needs at least 8" for 1x8 sides; more clearance lets you use 1x10. Then measure the footprint you want the trundle to occupy. These numbers drive every cut, so get them before you touch the saw.
Cut the plywood bottom to your figured width and to the bed length minus about 1-1/2" so it rolls in and out freely. In the source example that's 70-1/2" long by 38-1/2" wide. Keep the cut square.
Fasten the side boards around the platform, screwing into the ends of adjacent sides as well as into the platform edge so the corners lock. Pocket screws give the cleanest look; 2" screws and glue also hold. Keep it square.
Screw a caster to each of the four corners and two more in the center of the span — the center wheels carry the middle so a mattress and sleeper won't bow the bottom. Fill screw holes, sand, and finish so it glides on your floor. Confirm it rolls under the bed with clearance to spare.
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