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 Bluprint 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 »

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