To be able to determine how many stitches you need to cast on for your hat you need to first know your gauge and the desired circumference of your hat. First I’ll explain how to figure out those numbers and in the last chapter, I’ll give you the formula for the stitch count.
If you are not into math you can also knit your hats top-down and figure out the stitch count as you go. Here you can find a free top-down hat pattern.
How do I know the desired circumference of the hat?
Measure your head or use a size chart
If you are knitting the hat for yourself measure your head around the widest part above your ears and over your hair. Make sure the tape measure is snug.
If you are not able to measure the circumference (for instance because you are going to gift the hat) you can use this hat size chart to estimate the measurements based on age and gender.
Calculate the dimensions of your hat
Now that you know the measurements of the head the hat is going to be knitted for you can calculate the dimensions of your hat. Plain stockinette or ribbed hats should be worn with a little bit of negative ease meaning that the circumference of your hat should be smaller than the circumference of your head otherwise the hat will be sloppy. The rule of thumb here is that the hat should have approximately 10% of negative ease. You get this number by multiplying the circumference of your head with 0.9.
For instance, if the circumference of my head is 22″ (56 cm) the circumference of the had should be approximately 19.8″ (50.5 cm).
How do I know my gauge then?
What is gauge in knitting
In knitting, gauge means simply how wide one stitch is. The wider one stitch is, the less you need them to produce a piece of fabric that is for instance 4″ (10 cm) wide. Because it’s tough to measure the width of one stitch accurately, gauge is usually reported in stitches per 4″ / 10 cm or stitches per 1″.
Let’s take an example. If your gauge is 32 sts / 4″ (10 cm) the width of one stitch is 0.125″ (0.313 cm) and you need 32 stitches to produce a piece of fabric that is 4″ wide. If the stitch is narrower, let’s say 0.1″ then you need 40 stitches to produce a piece of fabric that is 4″ wide.
Did you know that it’s very likely that your gauge with certain needles changes over time
Did you know that it’s very likely that your gauge with certain needles changes over time as your technique develops? Usually, beginners tend to be tight knitters so they need bigger needles than the average knitter and when time goes by and they become more confident their stitches get looser and they need smaller needles to get the same gauge.
Also, the material (plastic, wooden, metal, etc.) and the type of the needles (circular, dpns etc.), as well as the yarn (material, yardage, plies), have an effect on the gauge.
How do I measure my gauge?
The only way to know your gauge is to swatch which many people don’t like because the swatches end up being useless (unless you knit hats top-down). But getting your gauge right is super important if you want a hat that fits well. To get a reliable measurement knit the swatch in the round and make it big enough.
Let’s take an example. I want to knit a hat with a circumference of approximately 22″ (56 cm). I usually knit a DK-weight basic hat with US 2.5 (3 mm) needles and I get gauge 23 sts / 4″ (10cm). With the previous numbers, I need a total of 22″ / 4″ * 23 = 126 sts for my hat. However, a quick look at Ravelry reveals that quite many people get gauge 21 sts / 4″ (10cm) with that needle size, and to produce a similar hat they would need 22″ / 4″ * 21 = 116 sts.
Now, if I went to Facebook and asked a person with that much looser gauge how many stitches should I cast on, the circumference of my hat would end up being 116 (her stitch count) / 23 (my gauge) * 4″ = 20.2″ which is 1.8″ (4.5 cm) more than I wanted to. That is quite much.
The formula for getting the correct stitch count
Now that you know your gauge and the desired circumference of your hat, you can make the calculations and determine the number of stitches you need to cast on.
If you have measured your gauge in stitches per 4″ use the formula below:
The circumference of your hat / 4 * (stitches per 4″) = total stitch count
For instance, my gauge is 23 stitches / 4″ and I want the circumference of my hat to be 22″ the calculation will be:
22 / 4 * 23 = 126 stitches (round up or down to next even number)
Or if you prefer centimeters (22″ = 56cm) and you have measured your gauge in stitches / 10 cm the formula looks like this:
The circumference of your hat / 10 * (stitches per 10 cm) = total stitch count