How to Knit the Right Hat Size, A Complete Guide

Knitting a hat is easy, until you end up with a hat that could fit a watermelon… Or a hamster. But we’ve got you covered! We have over two decades of experience designing hat knitting patterns, and with this guide, you’ll learn our best tips and tricks for how to knit the right size hat for anyone, whether for yourself or a newborn baby, and in any yarn you want!

Basic Hats For Everyone pattern in Plenty

Do I Need To Make A Gauge Swatch When I Knit A Hat? 

The short answer is, yes, you have to knit a gauge swatch! If you’re following a knitting pattern, you definitely need to make sure you’re knitting at the gauge your pattern recommends, adjusting your needle size or even yarn choice if necessary. If you’re designing your own hat, you’ll need your stitch gauge (number of stitches per inch) to determine how many stitches to cast on, and the round gauge (number of rounds per inch) to calculate how much length the crown shaping will take. Read our All About Gauge tutorial to learn so much more about this essential knitting concept.

And whether you’re following a pattern or making one up, your gauge swatch will also help you understand the qualities of your yarn and fabric, including how it stretches and does or does not bounce back! 

Choosing A Hat Size 

Measuring Heads For Knitted Hats 

Okay, with gauge out of the way (for now!), the next thing to think about is the size of the person’s head who will wear the hat. Head circumference is the most important data point for determining what size hat to knit, so, if possible, the first step is to measure that head!

Hat measurements shown on our free Box Hat pattern in Partridge Superwash

To measure a head for a knitted hat, you wrap a measuring tape around the widest circumference of the head, as shown above. The tape should run across the forehead, above the ears, and around the back of the head. Once you know that measurement, you simply follow along with the instructions for that size head (after knitting a gauge swatch, of course!). 

You can also determine the length of a hat by measuring from the bottom of the ears up to the very top of the head. That gives you the finished length for a close-fitting hat, or if the hat has a folded brim, the length of the hat with the brim folded. You can add some inches if you want a slouchy hat or one that stands up from your head a bit. Alternatively, you can always measure a knitted hat whose fit you like and want to emulate! 

Guestimating A Hat Size 

Choosing a hat size is a fairly straightforward decision when you can measure the recipient’s head, but when you can’t, these standard head size measurements from the Craft Yarn Council (the same measurements we rely on for our hat knitting patterns) will help you make a good estimate. 

Knitted Hat Circumference 

Hat knitting patterns, including ours, are sized by head circumference, but they also include information about the circumference of the finished hat. You might think that you want to knit a hat that’s the same circumference as your head, but it would probably fall right off if you did! Most hat knitting patterns call for negative ease, which sounds scary but just means that you want to knit a hat that’s a little bit smaller than your head, allowing the natural stretch of the stitches to hug your head for a snug fit. 

Exactly how much smaller the hat should be than your head depends on a few factors that we’ll get into later, but in general, you want to knit your hats with about 13% negative ease, or in other words, you want a hat that’s the size of your head multiplied by 0.87.  

Example: If you’re knitting a hat for a 22-inch head, you’ll do the following basic knitting math: 22 * 0.87 = 19.14 inches finished circumference 

Factors That Impact Hat Circumference 

Free Classic Ribbed Hat pattern in Cashmere Merino Bloom

• Stitch Pattern + Gauge: Stitch patterns with more stretch, like ribbing, call for a tighter hat than stitches with less stretch, like stockinette stitch. For example, the Large Adult size for our free Classic Ribbed Hat pattern is 16½ inches unstretched, while the Large Adult size for our free Nine-Note Hats pattern, all in stockinette stitch, is 20 inches. Also, if you’re knitting at a looser gauge for the yarn, you will also need to knit a smaller hat than if you’re knitting with the same yarn at a denser gauge. 

• Yarn Weight: The thickness of the yarn also impacts how much ease you need. Hat patterns using thicker yarns will call for less negative ease, or for a measurement closer to your head measurement. This is because, while you measure gauge on the outside of the fabric, the interior circumference measurement of the hat will actually be much smaller due to the thickness of the yarn and fabric! 

• Fiber + Spin: The qualities of the yarn itself can also have a big impact. Yarns made of elastic and resilient fibers, like merino wool, or with a tighter spin tend to hold their shape better and are less prone to permanently stretching out. More relaxed fibers, like yak and cashmere, or yarns with a looser single-ply spin can also make awesome hats, but they often work best with added structure or a tighter gauge. Our free Simply Hemmed Hat pattern in our Simply Yak yarn is a great example! 

• Desired Fit: Of course, you may want a hat that fits more closely or more loosely, depending on the style of the hat, your hair texture and style, or your own preferences, so keep those factors in mind, as well! 

Knitted Hat Length 

Everyone who’s ever knit a hat has asked themselves, “Is it time to start decreasing?” And most knitters will knit a hat that’s too short or too long in their lives, even if they’re following a pattern. But we have some tips to help you get it right!  

Crown Decreases + Gauge In Hat Knitting Patterns 

If you’re designing your own hat (or want to double check or alter your pattern!), gauge comes back into the picture when you determine where to start decreasing your hat. You’ll need to look at how many rounds the decreases will take and then work backwards from there.  

Example: If your round gauge is 24 rounds = 4 inches (6 rounds per inch), and you know that your crown decreases will take 18 rounds, you know that you should start your decreases when your hat is 3 inches less than your desired total length. 

Factors That Impact Hat Length 

Free Classic Cuffed Hat pattern in Daily Wool

• Cuffs + Hems: For cuffed and hemmed hats, you’ll need to knit a longer cylinder before you start your decreases. Your pattern should tell you how long, and you might want to fold your hat as you’re knitting to give you a better sense of the “real” length. Cuffed hats, like our free Classic Cuffed Hat pattern, are more forgiving than other styles, because you can simply fold the cuff differently to accommodate more or less length. 

• Crown Shaping: The style of crown shaping will determine how much length you need to knit before you decrease. Some hats decrease quickly, resulting in a rounded or gathered top, while others decrease more gradually for a pointy top. 

• Horizontal Stretch: If you’re knitting a hat that’s going to stretch a lot, like a ribbed hat that is much smaller than the head that will wear it, remember that when you stretch a knitted fabric horizontally, it gets shorter vertically. You’ll need to knit some extra length, and your gauge swatch is a good place to help you figure out how much. Just stretch the swatch how the hat will stretch and measure how much shorter the swatch gets. Did it get 5% shorter? Then knit your hat 5% longer! 

• Yarn + Gauge: Again, you need to consider the yarn you’re using to know how tall your hat will stand. If you knit a hat with extra fabric at the crown, using thicker yarn or a tighter gauge will cause the top of your hat to stand up, while a relaxed fiber or looser gauge will cause the top to slouch.  

• Desired Fit: You might want your hat to stand up, slouch, or fit closely to your head. Any of these can be very cute, but consider all of the above factors to knit a hat that looks just the way you want! 

Putting It All Together To Knit The Right Size Hat 

If you’re feeling like there are a lot of factors to consider for such a simple project, don’t stress! Well-written hat knitting patterns will take care of most of this for you. You just need to know the approximate head size of your recipient and your gauge, and the pattern should do the rest. But playing with these concepts will help you think more like a knitwear designer, not only ensuring a perfect fit but also giving you the knitting skills to adapt or even design your own hat patterns!

Basic Hats For Everyone pattern in Plenty

If you want to play with different hat styles using a pattern that does all the work for you, check out our Basic Hats For Everyone in Plenty pattern. It gives you lots of different styles all in one pattern for worsted/aran-weight yarn. The same pattern is also available in a light worsted/DK-weight version, so you have tons of yarn options! 

Ultimate Basic Hat Knitting Formula 

If all of this information has you totally excited to try and knit your perfect hat, we have a basic formula, with evenly spaced knit-2-together decreases for the crown shaping, that lets you design your own hat in any yarn you like. Give it a try and you’ll learn so much about hats along the way! 

1. Begin To Figure Out Your Cast-On Number: Determine your gauge (that means knitting a swatch in your hat’s stitch pattern and blocking it!), then multiply your stitches per inch by your desired hat circumference. For example, if your gauge is 5 stitches per inch and you want a finished hat circumference of 19 inches, multiply 5 * 19 = 95. This may be your cast-on number, but first… 

2. Consider Your Crown Shaping: In general, for your first round of crown decreases, you want to have about an 8 to 12 stitch repeat, with each repeat ending with a knit 2 together decrease. So, you need to make sure your cast-on number is divisible by a number between 8 and 12. If it’s not, you need to add or subtract a cast-on stitch or two until it is. In our example, 95 can be divided by 5 and 19, which would be either a 5 or 17 stitch repeat… Not ideal! And so, in this case, you would be better off adding a stitch and casting on 96 stitches, which is divisible by both 8 and 12. In this scenario, your best bet for the first round of crown shaping would be either [k6, k2tog] 12 times (a speedier and, therefore, steeper crown) or [k10, k2tog] 8 times (a slower, rounder crown). Great!  

3. Determine The Length Of The Crown Shaping: Typically, you will knit an even round between crown decreases until you have 2-4 stitches between decreases, at which point, you decrease every round to your final round of all decreases with no stitches in between. Going back to our example, let’s say we decided to [k6, k2tog] 12 times for our first round of decreases. Here’s what the crown shaping will look like: [k6, k2tog] + knit 1 round + [k5, k2tog] + knit 1 round + [k4, k2tog] + knit 1 round + [k3, k2tog] + knit 1 round + [k2, k2tog], [k1, k2tog], [k2tog] = 11 total rounds. So, now you can factor in your round gauge to determine how long your crown shaping will be in inches. For example, if your round gauge is 5 rounds per inch, the crown shaping will take 11 / 5 = about 2¼ inches. Keep that number in mind for the next step! 

4. Work The Body: Cast on and work all the way up to the crown shaping. Add a brim, a hem, a cuff, stripes, color blocks, whatever you want! Stop when the length of your hat is your desired finished length minus the inches you know your crown shaping will take based on your round gauge (and your step 3 calculations).  

5. Work The Crown: As already determined! 

6. Finish: Cut your yarn, thread it through the remaining stitches, weave in ends, block your hat, add a pom pom or tassel if you want, and you just designed and knit your first hat… And it fits! 

Now you’re ready to design your own hat or to tackle any hat pattern with the confidence that you’ll knit the right size hat that fits just the way you want. Explore our expertly designed hat knitting patterns and shop our amazing yarns to create a project that fits beautifully and is a delight to knit! 

Looking for more inspiration? Explore all of our free knitting patterns and knitting tutorials, buy one of our many knitting kits and yarn bundles, and shop for beautiful yarn. We have over 35 gorgeous natural fiber yarns in 100’s of magnificent colors, designed to bring integrity, beauty, and joy to your next knitting project and only available at Purl Soho!