What makes up gauge? Definition is number of stitches/rows in a given measurement, for example 16 dc/6 rows =4”, so 16 stitches of double crochet should equal 4” while 6 rows of double crochet should equal 4”. But now what do you do with it?
To determine if you will meet the measurements of the desired pattern the gauge is a tool to help you successfully execute this. But let’s understand why.
What you should get
I can see why knitters appreciate this so much more then crocheters…they have more stitches per inch typically. I happen to be looking at the back of a yarn skein that has recommended swatch gauge for knitting of 17s/23rows=4” and a crochet of 12sc/15row=4”, so using this gauge to fit a bust of 45” (a size L with some room, or an XL that fits snug) we would need 191.25 stitches in knitting and 135 stitches in crochet.
((number of inches in bust/number of inches in gauge swatch)*number of stitches intended in swatch)) =number of stitches needed
What you actually get
But what if we didn’t meet gauge and instead had an extra stitch per four inches (instead 18s/23rows=4” knitting, and 13sc/15rows=4” crochet) then our sweater would come out smaller by 3.75” then intended. In reality because of the size of the stitches, it is easier to add/subtract an extra stitch over 4 inches of knitting then in crochet, but it is still possible, and now our sweater has become a now snug fit L, and impossible to fit XL.
((number of inches in bust/number of inches in gauge swatch)*number of stitches actual in swatch))=number of stitches needed
So there is the importance.
Designing- How to get the stitches needed
If your are designing the gauge is the base for creating a sized pattern, or helping those using your patterns get the same results you did, as well as help determine how much yarn you need. For sizing the formula is basically the same as above.
((number of inches desired/inches in gauge)*stitches in gauge))=number of stitches needed
Designing- How much yarn do you need
Obviously, you can rearrange the formula with a little algebra and find any missing component, but this is a basic. To find the amount of yarn needed, you can determine how much yarn is in a swatch (that has a properly measured gauge), by either weighing it on a food scale or ripping back (or creating a new swatch and ripping back) and measuring the length of yarn used in the swatch.
You then determine the area needed in what you are creating, back to some geometry, for simplicity purposes well be using measurements for a 12”x24” tote bag. If our swatch is 3”x4” the are of the square is 3”x4”=12sq”, while the toe is 12”x24”=288sq”x2 (there are 2 sides)=576sq”,
Area=length x height
so now we divide by the area of our swatch 576/12=48, so we need 48 swatches to complete our tote. Now determine how much yarn is in our swatch, take the weight or the length and multiply by 48, this will be the total yarn needed. Compare this against your skein and determine how much you need to buy.
Total area needed/ total area of swatch= number of swatches needed
Number of swatches needed x weight of swatch (or length of yarn in swatch) = total yarn needed