Introduction: Make a Sidecar Cosleeper in 2 Hours With Standard Lumber.

About: I enjoy technology when it helps people. (And occasionally when it involves harmless pyrotechnics in the back yard.)

Co-sleeping with your baby is a great way to enhance bonding and makes it much easier to handle feeding in the middle of the night. However, pediatricians raise very legitimate safety concerns about sleeping in the same bed with your baby.

Our solution is a sidecar cosleeper that sits beside the bed, putting the baby right next to us, but with her own sleeping area so we won't accidentally roll over & squish her. I've made three of these over the years using standard dimensional lumber. You can make your own in a couple of hours.

Step 1: Materials & Tools

The materials and dimensions listed in this instructable are for a 38" X 24" mattress that is 2-1/2" thick. (This is the standard "compact crib" size.) You can easily adapt the design for any size mattress.


  • A compact crib mattress. Buy this first to make sure you know the dimensions. (I used the Kolcraft Cozy Soft Portable Crib Mattress:
  • 2 - 1 X 12 X 8' (clear, no open knots)
  • 1 - 1 X 4 X 8'
  • 3 - 2 X 4 X 8'
  • 2-1/2" screws
  • 1-1/2" screws

The lumber is dimensional lumber in US sizes.

When I made this, the lumber cost $30, the screws $7, and the mattress $25.


  • A saw to cut the boards to length. One board will need to be ripped to a narrower width, so a circular saw is ideal, but with patience, you could do this with a good handsaw.
  • A saw to round off a couple of corners. (You can do this with a jigsaw, bandsaw. or coping saw.)
  • A router with a 3/8" roundover bit.
  • A drill with a countersink bit to pre-drill for the screws and drive the screws.
  • A framing square.
  • 220 grit sandpaper.

Step 2: Let's Think About Safety Together...

You are ultimately responsible for the safety of your child, so you must decide for yourself what makes a safe cosleeper and only use this design if you are satisfied with it. To get you started, here are some of the issues I thought of when designing ours:

  • All furniture for babies should be clean and simple without anything to get tangled or hung up in.
  • All openings should either be much smaller than your baby's head, or much bigger than the baby's body.
  • Everything should be rounded.
  • Baby furniture should be stable, even if that means "heavy". Another approach to stability is to attach the cosleeper to the side of your bed with a hook & eye on each end.
  • The cosleeper mattress needs to fit snugly against the side of the bigger bed's mattress so there's no gap for an arm or leg to fall into. Consider attaching it to the side of the bed or using rubber feet if the cosleeper is on a hard (slippery) floor. (Thanks Malkenite, for the rubber foot suggestion.)
  • I decided to make the baby's mattress even with the adult mattress, but Vedubb points out that for added safety, you may want to consider putting the baby's mattress lower so the baby can't easily roll into the adult's bed.
  • Make sure any wood finish such as oil, varnish or lacquer is non-toxic. We just opted for no finish on ours, and that worked fine.

Think about anything that makes your house exceptional. For instance, we have large dogs, so I thought carefully about what happens when playing dogs crash into the cosleeper or decide it's their bed.

Please feel free to add your own helpful thoughts about safety in the comments area. That's the most welcome kind of comment.

Step 3: Figure Out How Long to Make the Legs

Measure the thickness of your crib mattress.

Measure the distance from the floor to the top of the mattress on your big-people bed. Subtract the thickness of the crib mattress from this, and then subtract another 3/4" for the thickness of the bottom board.

For instance, our crib mattress is 2 1/2" thick, and the top of our bed's mattress is 26 3/4" from the floor, so our legs are 23 1/2" long:


Step 4: Cut the Pieces Out.

The sketch shows you the dimensions of the pieces in an exploded view. When you choose where to cut each piece out of your boards, think about which surfaces will be hidden by the mattress, which surfaces need to be splinter-free for the baby's safety, and which surfaces should be pretty because they are visible.

Note: It might be hard to discern details on the sketches at the default display size, but if you click on the image twice (once to get to the viewer, and once to get to image detail), you'll get to a page where Instructables helpfully provides a link to larger image sizes.

Here's a complete cut list:

3 pieces of 1 X 12, 39 1/2" long.
2 pieces of 1 X 12, 24" long.
1 piece of 1 X 4, 39 1/2" long, ripped down to 2 1/4" width.
2 pieces of 2 X 4, 23 1/2" long.
4 pieces of 2 X 4, These are the legs. Cut them to the length you calculated in the last step.
1 piece of 2 X 4, 36 1/2" long.
2 pieces of 2 X 4 with a 45 degree angle cut on each end, roughly 12" on the long side.

Step 5: Round the Corners on the Sides

Pull out your two 24" pieces of 1 X 12, and decide which way you want to orient them on the ends. Then using a coffee can or something with a similar radius, mark a quarter-circle on the forward corners. Cut these carefully using a jigsaw, bandsaw, or coping saw. make the rounded edge as smooth as possible, because any little bumps will be amplified later when you use the router.

Step 6: Screw the Pieces Together.

Before you begin the assembly, look at all of the diagrams and pictures so you have the structure in your mind. In particular, notice how the front has a "lip" that extends beyond the legs slightly. This is to help snug the mattresses together.

It helps to have something like a big piece of cardboard or carpet to assemble this on so you don't scratch up the pieces that show.

Start by screwing the back to the sides. Use the 1 1/2" screws for this. Pick out the nicest 39 1/2" 1 X 12 piece for the back, since both sides show. The screws go through the back board into the ends of the side boards. I suggest drilling pilot holes for all of the screws that go into the 1 X 12 boards to avoid splitting them.

Then screw the three boards that make up the bottom to the bottom of the side boards. The bottom boards are the other two 39 1/2" 1 X 12's and the 39 1/2" board that you ripped down to 2 1/4". Put the narrow bottom board to the back. (Look at the end view to see how these are laid out.)

Take a moment to make sure this part came together well and make sure the mattress fits. If all is well, press onward...

Put the three horizontal 2 X 4 pieces on the bottom of the mattress box. Attach the two 23 1/2 side pieces first, making them flush with the back edge. You'll need to angle the screws slightly to screw down through the box into the 2 X 4's without scratching the sides, but it's not hard to do this if you're careful. When you attach the front 2 X 4 to the box, make sure you pre-drill all of the holes because it would be easy to split the board with all of the screws in a line. Finish this part by using a couple of the 2 1/2" screws to attach the end 2 X 4's to the middle one. You'll use the 2 1/2" screws for the rest of the assembly.

Now attach all of the legs, referring to the diagram for placement & orientation.

The two front legs don't have any braces, and depend on being snugly attached in the corner of the horizontal 2 X 4's for strength. Use the framing square to make sure they are on straight when you put the screws in.

Attach the braces on the back, making sure to pre-drill the holes, because it's tricky to hold everything in place while starting screws. Square up the legs with the square before attaching the braces.

Step 7: Round Everything Off With the Router

Use a 3/8" roundover bit in your router to round off both sides of the boards that make up the mattress box. It won't hurt to round off all of the boards, but the ones up on top are the most important. Adjust the depth of the bit so that it is as deep as it can be without leaving a bead (ridge) when you run it down the edge of a test board.

Make very sure you're happy with the depth by testing on scraps before you start routing the cosleeper. For most of the routing, you can run the router base on the flat part of the boards. When you get into the corners, you'll be on the short edge, but you should be able to guide the router by "bridging" to the other board in the corner. Having the depth set correctly will make the edges match up when you change the orientation of the router.

Practice for a few minutes on your scraps before you attack the sleeper you just spent so much time putting together. In particular, notice that moving in one direction tends to splinter the wood, but the other direction leaves a smooth edge.

When you're all done, use a piece of 220 grit sandpaper to smooth everything off. Be very careful to make sure there aren't any splinters on the side facing the baby.

I didn't put any finish on our cosleeper. If you decide you want to paint yours, be very careful to not use any toxic coatings.

Step 8: Use It!

When you place the cosleeper next to the bed, make sure the mattresses fit snugly together. The potential for a gap between the mattresses is a danger of this design, so it's important that you check this regularly. Make sure the cosleeper stays in place, and if there's any chance it will slide away from the bed, consider putting some screen-door hooks on the legs to attach it to the side of your bed.


Step 9: Some Other Designs to Consider...

Now that I'm getting feedback on this, I'm seeing some other nice designs that you ought to consider if you're making one of these:

(1) User plucas1 provided a similar design that would work for MDF or other "sheet" materials if you prefer them to boards. One advantage to his design is that there's no need to worry about bracing the legs. Check out his thoughts before you decide on your approach:

(2) Here's a great solution that one mom came up with to deal the problem of stability and attaching to the bed. If I used this design, I think I'd consider putting a spacer under the mattress, because I like having the baby at the same height as Mom & Dad. This design might be a little harder to remove for cleaning, but we found that we really didn't move ours around much.

(3) User FileBravo made a similar, and much prettier cosleeper using plywood panels:

(4) Instructables user Vedubb commented that for safety, his cosleepers are made to be slightly lower than the adjoining adult bed to keep the baby safely confined. Apparently he makes something similar (but more elegant) than this professionally in his shop, so you might want to look him up if you want to buy a finished cosleeper.

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