How To Modify The Size of a Crochet Hat Pattern

How to modify the size of a crochet hat pattern
I get a lot of questions about how to increase the size of my crochet hat patterns. I tend to crochet a hat for a specific person so I make only one size and when it's done I move on. Although I'm going to try and work harder at making more sizes for my patterns I wanted to share some tips on how to modify the size of a crochet hat. This doesn't just apply to my hats but to any hat pattern you find that doesn't have the size you need or isn't the right size once you finish it despite the size that was given in the pattern.
Option #1: Crochet the hat with a different hook size.
To make a hat bigger go up in hook size and go down a hook size to make it smaller. If the pattern calls for an I hook then try it with a J hook. Bigger hook= bigger stitches= bigger hat size. This method doesn't require you to modify a pattern so it is the easiest but you may not like the look of the stitches with a different hook than was recommended. This also will only work if you want to make a small modification in size. You aren't going to turn a baby hat into an adult hat by changing the hook size.
Option #2: Crochet the hat with a different yarn weight.
Sport, Worsted, Bulky will all create different size stitches. Even different types of worsted weight yarn create different types of stitches. Caron Simply Soft and Red Heart with Love will not create the same size stitches. I always pay attention to the type of yarn used in patterns I am crocheting because it's best to match the weight to get the right results. That being said you can also use a different weight to automatically increase or decrease the size of your hat without modifying the pattern. Like option #1 this isn't going to make a huge size difference but doesn't require any pattern modifications.
Option #3: Modify the pattern.
This is a little more complicated than option #1 or #2 and if you've never crocheted a hat before it might be hard to understand. If you have any experience with crocheting hats then you should be able to catch on.
Most hats follow a basic formula no matter what hat pattern you are using because you start off creating a circle. 
Start a circle by either creating a magic ring, crocheting into a starting chain or joining a set of chains. (How you start it doesn't matter as long as you start out with a circle)
Crochet a set number of stitches (8,9,10 etc)
Crochet two times in each stitch
Crochet once in the first stitch and twice in the next stitch. Repeat around the circle.
Crochet once in the first two stitches and twice in the next stitch. Repeat around the circle.
Crochet once in the first three stitches and twice in the next stitch. Repeat around the circle.
Crochet once in the first four stitches and twice in the next stitch. Repeat around the circle.
Do you see the pattern here? Do you know what the next line would be?
Crochet once in the first five stitches and twice in the next stitch. Repeat around the circle.
After the crown increases then the pattern is followed by crocheting once in each stitch around. This is the basic pattern for a circle no matter what stitch you use. Based on this formula you can easily add an increase to the crown of the hat. Keep in mind though that if your are going by stitch count you will have to adjust the next row of stitches.
Also, if you are a stitch counter (I am!) it's easy to figure out how many stitches should be in the next increase row. Figure out how many stitches you started with (8,9,10 etc) and add that to each increase row.
For example
Start with 10 stitches.
Rnd 1= 10
Rnd 2= 20
Rnd 3= 30
Rnd 4= 40
Start with 9 stitches
Rnd 1= 9
Rnd 2 = 18
Rnd 3= 27
Rnd 4= 36
There may be some deviation to the basic formula if you are not crocheting a regular beanie type hat. If the hat is a "slouchy" hat then it may be a little more complicated to modify after the crown increase. Also some pattern are crocheted from the brim up or in a square shape so the modification would not work for those.
Now that we've talked about modifying the pattern, how do you know what size your hat should be?
The easiest way to figure this out is to try the hat on your head (or your subject's head) as you crochet. Unfortunately that only works when your subject is readily available. If you are making your hat as a gift then you have to do some guesstimating. 
If you Google crochet hat sizes, there are lots of charts for hat size out there and they all vary a little bit. This one from Woolly Wormhead is one of my favorites.
I have found from personal experience that I like the look of hats that stretch to fit the subjects head. I like to crochet a hat a couple of inches smaller than head size to get the tight stretched look. For example, my head is 21 inches but when I make a hat for myself I will make it 19 inches because of stretch. On the other hand if I am making a hat for a baby I will only make the hat an inch smaller because that little head will grow very quickly and I want the hat to last as long as possible. 
Keep in mind what yarn you are using too because different types of yarn (cotton, acrylic, wool) have different amounts of stretch.
So now that you know what size hat to make, how do you know when to stop increasing?
I always keep a soft tape measure in my crochet bag because I use it all the time. You can measure the crown of your hat a couple of ways. I use the easy cheater way and measure around the circle. Usually I use a piece of yarn to wrap around the circle and then measure it with my tape measure.
The more accurate/mathematical way is to measure the diameter of the circle and multiply it by 3.14 (pi). 
What if one round is too small and next is way too big?
Now this gets a bit more complicated. If I really want to change the size of a hat, then I figure out the size of my stitches. 
Hat circumference divided by stitches = stitch size. 
Let's say I made four rounds of a hat with 40 stitches. The measurement of the circumference is 16 inches. 16 divided by 40 = .40. Each one of my stitches =.40 so now I need to figure out how many stitches would create the size I need. Let's say I wanted a 18 inch hat. 
Hat circumference divided by stitch size = number of stitches
18 divided by .40 = 45 stitches. So I know that I want my last increase round to be 45 stitches. This means that I will need to start my hat with 9 stitches and have four rows of increase to get to 45 stitches. The first round would be 9 stitches, 2nd- 18, 3rd- 27, 4th- 36, 5th- 45.
Not all examples work out so tidy so sometimes you will have few more or less stitches than is ideal.
Last, let's talk about the hat length.
This can tricky to get the right length but very easy to modify. I find that most charts give lengths that are too long so I usually go with the shortest recommendation. More stretch in the hat does require a little bit longer length though to make up for the stretch. It's easy to add a few more rows to hat if the stitches are all the same. If there is a variation in stitches (like in my crochet ribbed beanie) you may have to do a little guess work to add in the stitches at the right place in the pattern and still make it long enough. That's also why you should never be afraid to rip out (or frog) your stitches and try again. Modifying and designing patterns can take a lot of trial and error. If you are trying to finish something quickly it can be frustrating but it's also very satisfying when you get it right.
I hope this helps you to understand better how to modify a hat pattern and the next time you need a different size you give it a try. Let me know if you have any questions and I'll do my best to help!

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