How to Cut a Memory Foam Mattress

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Written by: Alex Savy
Read 13 minLast updated on February 22, 2023

Whether you want to reuse your old memory foam mattress or need to achieve specific dimensions, I’ve got good news for you: 

You can cut a memory foam mattress at home easily and with the tools you probably already have.

So, let’s learn how to tailor your old foam mattress to new dimensions and make it fit your needs perfectly. 

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What Knife Can You Use to Cut a Memory Foam Mattress?

Heavy duty tools to cut mattress

When it comes to memory foam, this material is quite pliant. Therefore, you won’t need to use any heavy-duty tools. A knife would do, but not just any regular knife. Here are the most common types you can use to cut a memory foam mattress:

  • Electric knife. This one is probably the easiest to use. You won’t have to make much effort and can simply slide the knife through the foam. Plus, using an electric knife is the most likely to result in sharp, clean edges.
  • Carving knife. A long, sharp carving knife is also a good option. With this knife type, you need to use short back and forth motions to cut through the foam.
  • Craft (utility) knife. Such knives are typically sharp enough to deal with foam. Plus, they usually have a pointy tip that can make it easier to go through the material. However, in this case, you should avoid sawing motions. Instead, start with a shallow cut on a small section of foam and then make the cut gradually deeper until you reach the bottom and cut through the foam. Then, you can move on to the next section.
  • Extra-large scissors. If you don’t have a suitable knife (or yours isn’t sharp enough), you can also use heavy-duty scissors. Cut smaller portions of foam and try to use only the tip of the scissors for a cleaner finish (and more precision).
  • Long serrated bread knife. If it’s sharp enough, a bread knife can easily deal with memory foam. You will have to use sawing motions to cut through the material. The edges may end up a bit ragged, but that shouldn’t be an issue if you plan to encase your mattress into a fabric cover.

Other Tools You Will Need

So, if you have bought the best memory foam mattress and don’t want to say goodbye to it, a couple of simple tools can help you transform it into something new (like an RV mattress, for example). Here’s what you might need:

  • a ruler or a measuring tape (to measure the needed dimensions);
  • a sharpie (to mark the lines along which you are going to cut your foam mattress);
  • a seam ripper (in case the mattress cover is not removable);
  • a sewing kit (to tailor the mattress cover to the new dimensions);
  • a drywall square or a piece of plywood/hardboard (to help you cut the mattress in a straight line and be more precise).

How to Cut a Memory Foam Mattress to the Desired Size

Now when you have all of your tools ready, you can start cutting your mattress. A quick word of warning before we begin, though: if you want to cut a memory foam mattress, you first need to check whether it contains fiberglass or not.  If it does and you start cutting, the fiberglass particles will be released into the room. And that can lead to very unpleasant consequences, to say the least (which may even affect your health) (1).

To find out whether your mattress contains fiberglass or not, read the description online or reach out to the company you have bought it from. If you learn that there’s fiberglass in your mattress, cutting it would not be an option. And perhaps in the future, you would like to consider one of the best memory foam mattresses without fiberglass

Also read: How to Pick the Best Mattress Without Memory Foam

Steps to cut a memory foam mattress

And if your mattress is safe to cut, here are the steps you might want to follow:

  • Take the mattress cover off. If it’s not removable, use the seam ripper to “open” your mattress up;
  • Place your mattress on a firm surface. You can use a layer of plywood underneath to avoid damaging your floor in case your knife crushes into it. If the mattress is thin and relatively lightweight, you may want to secure it in place by putting something heavy on the corners (like a couple of books, for example). They don’t have to be extra-heavy (to avoid damaging the foam), just enough to prevent the mattress from sliding off.
  • Determine the dimensions of the mattress that you want, measure it, mark the size, and draw the lines according to the new dimensions using a sharpie or a marker pen;
  • Cut the mattress without compressing the foam. Keep in mind that the bottom section of the foam may be of a higher density, which means you might have to make a bit more effort when you reach it. Also, when dealing with softer foams, it’s better to use a drywall square (or a piece of plywood) to avoid warping the mattress.
  • Trim off the excess bits if the foam edges turned out to be ragged. You can use a pair of scissors or a small knife;
  • Cover your “new” mattress with fabric. That’s when that sewing kit may come in handy. If you don’t want to sew, you can also use safety pins. Simply tighten the cover against the mattress, fold the excess fabric, and pin it all together (but make sure you don’t puncture the foam).

How to Cut a Memory Foam Mattress Horizontally

In case you need to make your memory foam mattress thinner, you can cut it horizontally. Allow me to warn you right away: cutting a foam mattress horizontally can be quite difficult. It requires precision and, of course, special tools.

Now, you have a few options here. The most common one is a long horizontal saw. Ensure you hold the top section of the foam but don’t press on it too much while gently moving the saw through the material. It might be a good idea to put your mattress on a sheet or a towel as some foam bits may fly around in the process. The fabric underneath the mattress will catch them, making the cleaning process much easier for you.

Some users note that you can also use an electric saw if you have one. However, it might be dangerous, so I believe it’s better to stick to a regular one. When using an electric saw, you may get hurt, especially if you try to hold the top section of the mattress to prevent it from sliding off while you are cutting. A regular saw is much safer in this case.

Another option is a hot wire (if you manage to find a wide enough model for your mattress). Keep in mind that this method requires an extra steady hand. Also, it might be more convenient for you to cut the mattress if you place it on a taller base. 

That being said, I personally do not recommend cutting your mattress horizontally. It’s the easiest way to damage the foam. Plus, there’s no guarantee your “new” mattress will feel comfy enough. Instead, you might want to consider getting a new one. I’m sure you can find a perfect thickness option among the best memory foam mattresses according to Reddit users, for example.


Is it okay to cut memory foam?

Yes, it should be okay as long as you are gentle with it. Just try not to compress it or apply too much force when using the knife to prevent damaging the texture of the material.

Can you cut memory foam with a hot knife?

Theoretically, you can, but using a hot knife can damage the foam and might make it lose its shape. A regular knife is enough if it’s sharp enough, so there’s no need to use a hot knife, really.

Can I cut a gel memory foam mattress?

Yes. The gel particles are infused with foam, so you don’t have to worry about gel leaking in the process if you decide to cut your mattress.

How do I Cut Memory Foam with a Hot Wire?

The best way to cut memory foam with a hot wire is to take the memory foam outside, turn on your hot wire cutter, and make cuts where you need them on the memory foam. Memory foam cuts easily on a hot wire, however, due to the wire melting a bit of the foam, hot wire cutting should always be done in a well-ventilated area to avoid exposure to fumes.

How do I Cut up a Memory Foam Mattress for Disposal?

The best way to cut up a memory foam mattress for disposal is as follows:

  • Lay the mattress on a plastic sheet or take it outside.
  • Remove the piping with a knife.
  • Remove the cover and side panels with a knife, taking care to avoid staples.
  • Separate the memory foam and foam core layers and cut them down individually with a knife, larger scissors, or a small saw.
  • Put the small pieces of memory foam into plastic bags for disposal.


Who says you can’t make a custom-size memory foam mattress at home?

All you need is a sharp knife and a trusty ruler. And yes, a bit of time. But as a result, you can get pretty much any mattress dimensions you want. Just make sure you treat the foam carefully and don’t compress it too much in the process. After all, you will need your “new” mattress to retain its properties, right?

Why do you need to cut your memory foam mattress? Are you trying to achieve any particular size or a peculiar shape? Let us know in the comment section below!


  1. Washington State Department of Health (n.d.). Fiberglass. Retrieved from 


  1. its 3 to 4 inches goes under the head board

    1. Hi Anthony,
      If I understand your comment correctly, I would advise you against placing memory foam under the headboard, as it can damage the material.

  2. To make king size sleep number into separate beds together so one size can be up without bugging person on other side of mattress

    1. Hi Roger,

      Apologies for the delay! It sounds like you’re splitting a king in half, which is a type of bed setup called a ‘split king,’ which allows two people to sleep together with less motion transferring across the mattress due to the split.

  3. my child’s bed is a bit shorter than a queen mattress size so I need to take a small amount off one end to make it fit

    1. Hi Gill,

      Apologies for the delay! For sure, making it a bit shorter shouldn’t be a problem using the tools and tips I suggested above, like the electric knife, and ensuring the foam isn’t compressed while being cut.

  4. I am all alone and my king bed is depressing.

    1. Hi Matt,

      Apologies for the delay, and I’m sorry to hear about it. If that’s the case, it may be time to replace your mattress. Often, there are disposal companies that can come take the old mattress away, and getting a mattress with white glove delivery can help ensure the delivery people put the mattress where it needs to go.

  5. My husband and I are not comfortable sleeping on a 3” gel foam mattress. Would it be possible to put it under our king size mattress?

    1. Hi Sue,

      Apologies for the delayed response. As convenient as it sounds to put one mattress on top of another, the bottom mattress would become crushed and unusable under the extra weight in the long run. If you want to soften out the gel foam mattress, you could consider getting a soft topper to give you a few extra inches of cushion.

  6. Cutting a few inches off of a full size mattress so it can fit sideways in my camper van

    1. Hi Ryan,

      Sorry for the late reply! That sounds fantastic, I hope it works out!

  7. I would like to cut the mattress pad to
    make cushions for my deck chairs

    1. Hi Al,

      Thanks for reaching out! As long as you measure the mattress pad for the right size of cushions for your chairs, taking a tool like an electric knife should get the job done efficiently. Good luck with your deck chairs!

  8. Desperately seeking a 6-8″ gel/memory foam mattress that I can cut for my Sprinter van and one that DOES NOT have fiberglass. Ugh. Struggling. Most are thicker than 8″. Any thoughts?

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