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Knitting Math 101: How to Calculate Stitches in Knitting

So you finally mustered the courage to design and stitch a hat. Yay, you! Designing your own knitting projects opens up endless possibilities in your knitting. No longer confined to other’s knitting patterns, you can play with new stitches, experiment with shaping, and get the perfect fit.

Figuring out how to stitch a hat isn’t easy at first, though. Knitting math can be intimidating. Let’s start with the most basic issue when learning how to stitch a hat: How do you calculate the number of stitches to cast on?

True Lace Hat knitting pattern

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How to stitch a hat from scratch

1. Measure your head.

Break out that measuring tape! The first step to achieving a hat that fits you perfectly is to measure the circumference of your head, (If you’re like me and have a big head with a lot of hair, you dread the results of this measurement).

Wrap the measuring tape around your forehead and the full circumference of your head. Pull the tape as taut as possible. Remember: you don’t want your head to fall over your eyes. Write this number down so you don’t forget it!

I actually like to round the head circumference number down just a bit to make sure my hat fits snugly on my head. I usually round down about 2″, but this is based on personal preference. So for example, if your head circumference is 22″, round down to 20″ to give yourself a two-inch ease. This will ensure the hat isn’t slipping over your eyes or off your head when the wind blows! If you want your hat to fit more loosely, you could round down just one inch.

Measuring gauge in knitting

Measuring gauge

2. Measure the gauge.

Have you already chosen the yarn you’re going to use? Great! The next step is to swatch that yarn.

Check out the yarn label and see what needles work best with the yarn. This will depend on the weight of your yarn. Don’t have a label? Take a guess at the yarn weight and experiment with a few different sizes of needles. Remember that for a hat, you want the stitches to be close together so that the hat will fit snugly to your head.

Once you’ve found a needle size you like, knit a swatch. The larger the swatch, the more accurate the measurements, so try to knit a swatch that’s several inches in width and height.

Now you need to figure out how many stitches per inch you have. Use a ruler to measure how many stitches fit within one inch. Write that number down.

3. Multiply.

Multiply the head circumference from Step 1 by the number of stitches per inch in Step 2. This is your number of stitches you will cast on. Ta da! You’re finished!

The cheater’s way

If you’re totally overwhelmed by knitting math, I’ve found that using a hat calculator is a good option. I love this simple hat calculator from Earth Guild, one of my favorite local fiber stores. (If you’re ever in Asheville, North Carolina, you should definitely plan to stop in!) The calculator has a chart that includes stitches per inch variables from 2-6, along with how many stitches to cast on for six different head circumferences. The hat calculator can also help you through the dreaded task of making even decreases when the time comes to shape your hat.

Get the simple hat calculator here.

Did you drool when you saw the True Lace Hat at the top of this post? Me, too. The pattern is available exclusively to Craftsy members enrolled in New Directions in Lace: Hats with Kate Gagnon Osborn and Courtney Kelley. You’ll not only get patterns for three gorgeous lace hats, but you’ll also get tips for changing the length and circumference of any knitted hat.

FREE Guide: Knitting Abbreviations You Need to Know

knitting abbreviations

Download this exclusive one-page guide and never get stumped by a weird abbreviation again.Get my FREE guide »

11 Comments

May Goose

Craftsy is a brilliant site for all crafters, knitters, sewing fiends and generally anyone who likes to make and do projects with yarn, material, patterns or needles

Reply
May Goose

Craftsy is a brilliant site for all crafters, knitters, sewing fiends and generally anyone who likes to make and do projects with yarn, material, patterns or needles

Reply
Martha

Good site ,thank you.

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Aubrey

If you cast on however many stitches your calculations come to, how do you figure the amount of decrease stitches for the top? The cast on number has to be evenly divisible for a gradual decrease and not all cast on numbers will work, unless you add or take away a certain number of stitches before beginning the decrease rounds.

Reply
Julia

Earlier this year, I learnt to knit my first project – a ‘patchwork quilt’, consisting of 90 squares of varying (so far knit/purl) patterns. Basically, I was receiving a new stitch for the square every month but had to cancel my subscription. So, the question is how do I work out how many stitches to cast on to achieve the correct square size? Thanks guys!

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Jenn

What a great resource! I know math, any type of math, is intimidating to me, but this breaks things down well.

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Althea Murcko

I already have Mrs. Crosby steamer trunk yarn that I bought for another hat that I wasn’t liking. Can I use that yarn for one of the lacy hats.

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Phyllis

How many stitches do you cast on to knit a hat for a baby with a head circumference of 15 inches? I have looked everywhere and have yet found what I am looking for, Would appreciate a reply from anyone who may know the answer to this……………..thanks very much

Reply
Suzana

Number of stitches per 1 inch x 15 inches = number of stitches you need to cast on in this case

Reply
Eva

Hello 🙂
I wanted to know how to do the same thing in centimetres?

Reply
Jaden

Count the number of stitches per 10 cm. Measure your head. Substract 2.5 to 5 cm from the total to get a snug fit (negative ease). Multiply stitches with that number and divide by 10.

Example: 20 stitches per 10 cm, head circumference 55 cm, negative ease 5 cm
1.) 55 – 5 = 50
2.) 20 x 50 / 10 = 100

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