I bet you are going through a nice woodworking project (maybe a tabletop, a picture frame, a bookshelf, or a drawer), and you decided to use a biscuit joiner to join the pieces of wood together. But then, a question arises: what biscuit size should I use for the joints?
Here’s the quick answer: if you are looking for strength in your joints, then you should use the largest biscuit possible. Instead, if you are using the biscuits for alignment only, you can use whatever biscuit size you want. If you wanna know more about biscuit sizes and how to choose them in different situations, don’t miss the rest of the article!
Biscuit Size Chart and Uses
You may already know this, but just to make things clear, a biscuit is usually an oval-shaped, highly dried and compressed wooden piece. Here I made a quick table, showing you the common biscuit sizes you can find in almost every store:
Biscuit Size Width Length
FF 1/2" 1-3/8"
#0 5/8" 1-7/8"
#10 25/32" (~3/4") 2-1/8"
#20 15/16" (~1") 2-1/4"
The most common ones, going from the smallest to the biggest, are FF, 0, 10 and 20.
- FF (which are 1/2 inch by 1 3/8 inches) are the smallest ones, and they can be used for small projects. We will talk about these later on since they are kind of special ones;
- #0 (which are 5/8 inch by 1 3/4 inches) are used for bigger workpieces that FFs, but they can not bear a lot of tension. They should be used for projects like picture frames, where there’s not a lot of stress applied, or narrow applications, where you can’t fit bigger biscuits;
- #10 (which are 3/4 inch by 2 1/8 inches), are the standard size that you can find not only in specialty stores but also in home centers. These are suitable for most of your woodworking projects and can stand quite a bit of stress.
- #20 (which are 1 inch by 2 3/8 inches), are the biggest you can find on the market. These are the big boys: they can stand a lot of weight, and they can be subjected to a lot of stress. You can use these if you are working on a tabletop, a drawer, or something that will undergo a lot of use over time.
What Biscuit Size to Choose
As I said earlier, there are mainly two questions to ask yourself when choosing the size of the biscuit to use:
- Am I looking for strength in my joint?
- Am I looking for alignment for my joint?
If you answered yes to the first question, then you should use the largest biscuit you can fit where you intend to place the joint. There is a simple way to check this: just take your biscuit joiner, and press it against the border of the surface where you are going to make the joint. Then check how much of the blade comes out: as long as there is enough material between the end of the blade and the opposite edge of your board (let’s say 1/4 of an inch), you are good to go. If you have less than that material left, then it’s safer to choose a smaller biscuit size. Instead of using a bigger biscuit, you are gonna use as many biscuits as you can fit along with your wood board.
If you instead answered yes to the second question I asked you, then pretty much any size will do the job for you. Use an adequate number of biscuits to get the job done. If you asked me what size to pick, I would say the smaller the better, especially if you were working with narrow boards. In this case, you should consider FF biscuits. Let’s talk about those.
What are FF biscuits? Should I use them?
I think you are going to agree with me when I say that biscuits are a great joinery solution. But like all things in life, they do have some limitations. One of them is the length of the slot that is required to put a biscuit in place. As you can see by yourself if you look at the chart I posted before, even the smallest biscuit, the #0, needs a slot that could be too big for certain spots. That’s the reason why they came up with FF biscuits.
FF (that stands for Face Frame) are smaller biscuits, and they have a rounded form, instead of an oval shape. This way they take up less space, and so they can be used for smaller workpieces. That’s great, right? But unfortunately, there’s a problem.
To use these smaller biscuits, you need a smaller slot: biscuit joiners usually come with a 5-inch diameter blade, and you would have to change it to a smaller cutting blade. Not all the machines let you do that: chances are that if you have a DeWalt joiner, you can’t put on a smaller blade. If you have for example a Porter Cable plate joiner, then you can easily swap to a smaller blade.
In conclusion, if your joiner doesn’t let you change to a smaller blade, you aren’t going to be able to use FF biscuits.
What Biscuit Size should I use for 1/2 Plywood?
The quick answer is the following: If the quality of the plywood is good, you can use up to #20. Otherwise, you should stick to #10.
If you are making a piece of furniture with plywood, chances are you want your joint to be clean and invisible. Biscuit joint might be the answer you are looking for. When we talk about plywood, there are two things to consider:
- the quality of the plywood;
- the thickness of the plywood.
If the plywood is cheap, there’s a risk that the biscuit will swell too much, deforming the surface. In case you are working with quality plywood (let’s say 7 ply plus), then you should be fine. If you are not sure about the quality of your material, you could try making some joints with some plywood scraps, let them rest for a week or so, and check if any problems come out.
The second factor I mentioned is the thickness of the plywood. In this circumstance, we are talking about 1/2 inches plywood, which is quite thin material. In this case, you need to make sure that the material is good, so you should go through the process I explained a few lines above.
What Biscuit Size should I use for 3/4 Plywood?
In this case, we are working with thicker plywood. Either #10 or #20 size biscuits should work fine with 3/4 plywood. Again, if you are not sure you are working with quality material, and the project you are working on is important, you should go through the process I explained in the paragraph before, and make sure to avoid unpleasant surprises later on.
In the end, you should be fine using #20 sized biscuits.
How many biscuits should I use to join wood?
Now that you learned all there is to know about biscuit sizing, the next logical question to ask this one: how many biscuits should I use to join my pieces of wood?
In short, you should use as many biscuits as you can fit in if you are looking for a strong connection between the parts; instead, if you are using the joint for alignment purposes, a good rule of thumb is using a couple of biscuits per foot of wood.
In the end, it depends on the type of project you are working on: for something that requires certain stability, like a tabletop, you should space them pretty close, at about 6″- 8″ on center. If you are working on something that doesn’t require that much strength, for example a picture frame, you could space them wider, at around 10″ – 12″ on center.
It also depends on the thickness of the material: you can go with double biscuits in thicker material ( what I mean is creating a slot which is two times wider, so you can put in two biscuits together).
In this article, you learned all you should possibly need about biscuit size for your woodworking project: first of all, what sizes are available in the market and a couple of rules to identify the right biscuits for you (always ask: am I looking for strength in my joint? Or it is just a way to keep things in position?). Then we looked at possible applications of various sized biscuits (we also discussed FF biscuits). The next point I wanted to get to you is the importance of considering what type of material you are working with, and his thickness. Finally, I answered the question: how many biscuits should I use to join 2 pieces of wood?
In short, the key points of this article are the following:
- Use the largest biscuit size possible;
- If you are not sure about the quality of your material, try to make some joints on scraps first;
- You can use FF biscuits only in you have a plate joiner that let you swap blade to smaller ones;
- Use as many biscuits as you can fit in to join two pieces of material.
That’s all for this article, I hope that now you have a clearer idea of what biscuit to use for your project. It’s time to get to work now!