When you use all capital letters when you are writing it is often read as shouting. A simple "hello" comes across as much more alarming when it is written "HELLO." With that in mind, I will say this post is about making a knit SWATCH. I do not mean to shout at you, but every time I read the word swatch, I read it as though one of the knit gods is shouting at me to, well, swatch.
Making a swatch has a bad reputation, I think, because it takes some time to do it well and the end product is nothing exciting. You've picked a pattern, you've purchased the yarn, why the hell do you want to spend an hour or two making a swatch? You want to dive right in to your project, of course. You want to skim right over that pesky little phrase that pops up in nearly every pattern to use a particular size needle "or size to obtain guage." Why not just go ahead and use the same size needles the designer did and call it a day?
With some patterns you can plunge blindly forward with the prescribed needle size (don't forget to check the weight of your yarn). Sometimes a pattern even states it does not matter too much, especially with shawls, scarves or cowls that can be knit in different weights or sizes with the same pattern. I've even seen a few hat patterns that are written to accommodate our seemingly inherent and visceral dislike of swatching. I would highly recommend you treat yourself to a pattern like this every once in a while. But, and this is a big ugly but, never become complacent about swatching. There are many good reasons to do it, and while we are all good at making excuses not to, at the end of the day swatches actually save time. Gasp.
Gauge is given in a pattern so you know how many stitches there are within a set of inches or centimeters. This matters because it is how the designer made their calculations to obtain the size of their finished product. It wouldn't really be crazy to think that if you use the same yarn and the same needles as the designer you should get the same results. And you very well might. However, you might not. Every knitter is different. We all have our own special way of knitting. I do not mean this in a technical sense, I mean it more in a personal sense. As you knit, you develop a relationship with the fiber you are using. This might sound like crazy hippie lady talk, but it's not. Your relationship with the fiber is uniquely yours and this may lead your stitches to be slightly tighter or slightly looser than the designer's stitches. The only way to know is to make a swatch.
Especially if you are making something where the size matters (*ahem*), you want to make sure your gauge is correct. And "close enough" is not enough. If, for example, when you knit four inches and you have one less stitch than the designer, you would be fine in the short term. One stitch off? Who cares? But imagine you are making a sweater that has a 32 inch circumference. That one stitch has suddenly become 8 stitches by the end of your round. That could seriously effect the way your garment fits or drapes. And that is just a little difference. Imagine if you are four or more stitches off from the designer. I shudder to think. And no, people will not believe you that "that's the way it's supposed to look." There is only so much shrinking or stretching a good blocking can do- don't test the knitting gods that way, it's not worth it.
So, let's say you make a swatch and you do discover, whether because you are using a different yarn or you have slightly different stitch-tension from the designer, that your stitch count is not the same as theirs. What do you do? Well, that is where that phrase comes in..."or needle size to obtain gauge." You simply need to find the needle size that gets you on track with the designer. Typically, you only will need to move up or down one needle size. There are exceptions, though, so be patient and make sure you do your due diligence when making a needle size adjustment.
Making a swatch is not only important for gauge. It also helps you to see if a yarn selection is a good one for a given project. When you make a swatch, you can see if the stitch definition, color, and drape are what you were looking for. It's much easier to take an hour to make a swatch and change your mind about a yarn than it is to finish a whole project and realize you don't like it or the it's not quite right.
A hint, though...keep your swatches if you can. (Sometimes you may be desperate for that last little bit of yarn to finish a project and have to sacrifice a swatch, and that's okay, too.) Label each swatch with the yarn you used and the needle size. If you are using a fancy stitch in your swatch, keep track of that, too. The more you knit, you will begin to build a reference library for yourself. It will help you make smarter decisions about yarn for your projects, fiber and color choices will become easier, and you will begin to feel like your swatches really are good for something and a bit more satisfying to make.
It is a pain, there is no doubt about it. But taking the time to make a swatch can save you a whole lot of grief, my friend. Take it from a knitter who has tried to get around it and learned the hard way how important it is to do a little prep work. And that is why every time I see the word "swatch" I read it as "SWATCH." Heed the shouting.