Is Your Bed Frame Too Big? Fix it in 30 Minutes


What to put between mattress and bed frame is a common question people ask after they purchase a new box spring and mattress. We spend about one-third of our life in bed so when we purchase a new box spring and mattress and get it home we are super excited!

We have several DIY fixes so you know exactly what to do if the bed frame is too big for your new mattress in 7 steps if your mattress is too short and 7 steps if the bed frame is too wide for the mattress.

Mattress is Too Short: Extend Mattress

There are two options to extend the length, the bottom or the top of the mattress to fill in the gap. You can fill the bottom of the bed frame with wood up to the top of the mattress, but that may not feel so good when you flip onto your tummy at 3 am and drive your toes into the lumber.

Ok, so maybe filling in the top of the bed frame is a better idea since that area is usually covered with pillows to protect your head. If you use a topper it may fit over the mattress wood filler.

If you have to pull out the saw you may want to build a cheap one from scratch so you can make one that is perfect for you. Read my article here to see if this is best for you.

Now determine the filler material. If the gap is 1.5” or 3.5” you can purchase the lumber, a 2” x 4” (5 x 10cm), and fit them into the gap.

For a 3.5” gap follow these 7 steps:

  1. Measure the width of the bed frame opening.
  2. Measure the height to the top of the mattress.
  3. Cut boards and insert the first one into the bed frame at the top (head).
  4. Add a second board and screw it to the first board to secure it firmly.
  5. Add additional boards until level, or almost level, with the top of the mattress.
  6. If there the boards do not reach the top of the mattress you can simply add strips of plywood.
  7. Since this area is under the pillows I don’t think it needs to match the mattress height exactly… but I am not OCD so I am not sure if this is accurate enough for you (if you are OCD and cannot accept this imperfect solution your next option is to go buy a new bed frame to match your mattress).

For a 1.5” gap follow the same steps above except installing the lumber on edge. Fasten with longer screws toe-nailed (toe-screwed???) to hold it all together. Add several tow-screwed screws on the ends of the lumber for the best holding strength.

Cut lumber to fit for other gap sizes.

Bed Frame Too Wide for Mattress

The solution to a bed frame that is too wide for a mattress is a little more challenging, but it can be conquered. I know I don’t want to roll over in the middle of the night and fall between the frame rail and the mattress so let’s consider a few options.

Box spring and mattress combination: The box spring is not supported if it does not sit on the bed frame so some structural work is required:

  1. remove the box spring and mattress… sorry. I know you just bought the new bed and are dying to try it out, but this won’t take long.
  2. Measure the width of the bed frame opening and cut lumber to sit on the bed frame. The lumber can be spaced with a 12” gap as the box spring frame is wood and reasonably strong.
  3. Pop the box spring and mattress back on the frame and test it out. Make sure it is strong.
  4. The mattress is now 1.5” (4.5cm) or 0.5” (1.25cm) higher depending on if you used lumber or plywood. If that is an issue please see this article to fix.
  5. Now you have to address the hazard of the wider bed frame. Waking up groggy and jumping out of bed can be dangerous. One solution is to fasten a body pillow to the side of the mattress while resting on the extended box spring.
  6. Another option is to split the difference with the box spring and mattress in the center of the box spring.
  7. Another option is to fasten lumber on a 45-degree angle so your feet slide down the lumber to avoid the sharp edge of the extended bed frame.

If you have a bed frame model with cross members attaching in the center you can drill new holes large enough to access the double pins to hold the cross members together. Simply measure the width of the bed frame and the box spring or mattress and mark the difference on the cross members and drill new holes. Easy solution and if you don’t have a drill and drill bits invite your construction friend over on Saturday for a few beer and a BBQ… and ask him or her to bring a drill.

Another simple solution is to add lumber to fill the gap the same as we did to the head of the frame above. The easiest way for this to work is to push the bed against a wall on the left or right. Pull the mattress out to the edge and fill in the void against the wall, which will prevent the mattress from sliding around.

If you need to adjust the height of your bed frame please see this helpful article here.

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Scott Boyd

A semi-retired workaholic in Thailand is a challenge. It is too hot to keep building adobe and earthbag buildings so a new project was needed. I became interested in bed frames after purchasing a bamboo bed frame from a local supplier here and I learned there is little information about them on the Internet. So now I spend my days researching, testing, and reporting my findings to help others while having an occasional beer and istening to 60s and 70s B side rock, blues, and much more.

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