Convex & Concave
When your crochet is shrinking or fanning out, and you know you aren’t losing or gaining any stitches, it’s because your tension is changing. Tension is how tight or loose you hold your working yarn. Having tension issues throughout your work is fairly common, especially with people that are learning the basics of crochet. Here, we’ll explain what is happening and how to correct it. Note: If your rows aren’t curving but are still Narrowing & Widening, check out that link for a solution.
Convex
When your crochet is convexing, your tension is getting looser as you work. The first few rows will start out tight, but as you crochet more rows, your tension becomes looser. The looser your tension, the larger the stitches, and that’s why your rows seem to fan out wide.
Concave
When your crochet is concaving, your tension is getting tighter as you work. The first few rows will start out loose, but as you crochet more rows, your tension becomes tighter. The tighter your tension, the smaller the stitches, and that’s why your rows seem to shrink in on themselves.
The best way to fix tension issues is to practice tension consistency. It sounds a little complicated, but all you’ll want to do is try and hold your working yarn with the same grip the entire time you crochet.
Get any yarn and hook you have or are comfortable with, make a chain however long you want (between 20-40 would be great), and start crocheting. Make sure you’re using the same stitch throughout your practice. This will make sure that the only variable changing the size of your project is your tension. If your tension starts out one way and changes, don’t stop. You’re going to keep on crocheting until you feel like your tension has been consistent (even edges) for several rows and you don’t have to think much about how tight or loose you’re holding your yarn.
Once you get to this point, you’ve discovered your natural tension. This can take you a few rows to find, or you could make a 20’ scarf before you find it. Either way, once you get nice even edges, you’ve found the tension that’s most comfortable to you. It could be tight or loose, but all that matters is that it feels natural and easy to keep that tension consistent.
At this point, you can start going into a new project, or start over trying to either keep even tension from beginning to end, or practice tension consistency with a different stitch. No matter what you do after this practice project, remember how your hook and yarn felt as you work with it to get that same tension.
If after this, your starting tension is different than the rest of your work (even when your work is even throughout after your first few rows), you’ll need to practice the muscle memory of keeping even tension a little more. For the time being, you can make a swatch until your tension is even and then start a project. Or try making a chain, crochet a few rows until your work is even, frog the whole thing and do it again and again until your starting tension is the same as your normal tension.
At the end of the day, your tension is one of the basic things you will have to work on regardless of the project. Having even tension will make your projects so much nicer and neater, and you’ll feel so much more confident and secure in your crochet skills.