Increasing and Decreasing: Amigurumi Math

So you want to design your own amigurumi. Hopefully, you’ve already looked at my first post of tips. If you’re ready to start increasing and decreasing in non-standard ways, it’s time to learn a little bit of math. I know math wasn’t most people’s favourite subject, but it’s really helpful to tell you how to increase evenly to however many stitches you want in the next round.┬áSure, you could always use the basic sequence of increases, and have all of your rounds worked as 6 stitches, then 12, then 18 etc, but that doesn’t give you much flexibility. What if you want to go from 12 stitches to 15? Well, you should increase every fourth stitch. But how did I figure that out?

The math isn’t difficult. You just need to know how to multiply and divide (It’s helpful to know your multiplication tables, for speed). If you want to change the number of stitches in a round evenly, you need to find a factor of the current number of stitches. Maybe you don’t remember factors from school. That’s alright, that’s what I’m here for. Factors are just numbers that divide evenly into the number you’re finding factors of.┬áTake a round that has 20 stitches in it. The factors of 20 are 1, 2, 4, 5, 10, and 20. You can divide 20 by any of those numbers, and end up with a whole number.


Because 2 is a factor of 20, you could put an increase in every second stitch, and go from having 20 stitches in a round to having 30. 20/2=10, so you would get to increase 10 times, and would add 10 stitches to the 20 you already have. You could also increase every fourth stitch, because 4 is a factor of 20. In that case, because 20/4=5, you would increase 5 times, and the next round would have 25 stitches. In fact, you could increase every 5th, 10th, or 20th stitch to: any factor of your current stitch count.


Decreasing is a little different. Since 4 is a factor of 20, The 20 stitches can be divided into groups of 4, 5 groups, to be exact. To turn those 5 groups of 4 into 5 groups of 3, you want to decrease every third stitch. As a basic rule of thumb: take a factor of the number of stitches you have and subtract 1. That’s which stitch you should decrease on. To calculate how many stitches the next row will have: divide the total number of stitches by your chosen factor (e.g. 20/4). Take the answer (in this case 5), and subtract it from the number of stitches you started with. This gives you 15, the number of stitches you’ll have if you decrease in every third stitch.

The math might still seem intimidating, but you’re sure to get it with a little bit of practice. Before I worked out how the math works, I spent a lot of time thinking really hard about where to increase and decrease to make the shapes even. Even if you don’t vary from the usual 6, 12, 18 pattern very often, it’s really helpful to be able to do it easily when you want to. Feel free to ask me any questions you have about making amigurumi, and I’ll try to answer them below, or else in another post.