How to Determine Adult and Children’s Hat Sizes

When knitting from measurements, one of the hardest questions is how to choose the right size. It can be especially tricky with hats, house slippers (where the instep matters), and garments for girls and women (where bust and hip measurements matter). Taking the measurements is straightforward, but how should you use them in your knitting?

Start with the Hat

I searched through countless charts and articles online. In the end, I pieced together the information through trial and error, and now I am sharing it with you.

Measurements

Head Circumference

Measure around the widest part of the head, following these points:

• 1 cm above the eyebrows
• the most prominent part at the back of the head

Crown Diameter

To estimate the diameter of the crown—the section at the top of the head—divide the head circumference by 3.14. For a snug fit, subtract 1–2 cm from the result. The exact adjustment depends on:

• how much the stitch pattern stretches
• your knitting gauge
• the yarn or other material

Hat Height

Measure from one ear to the other over the crown of the head. Divide that measurement by two, then add 1.5–2.5 cm, depending on how fully you want the hat to cover the ears.

Approximate Size Chart

The original chart lists head circumference, crown diameter, hat depth when laid flat, and approximate age. Its values are translated below:

• 0–3 months — head circumference 36–40 cm; crown diameter 11.5, 11.8, 12.1, 12.4, or 12.7 cm respectively; hat depth 12–14 cm
• 3–6 months — head circumference 41–44 cm; crown diameter 13.1, 13.4, 13.7, or 14.0 cm respectively; hat depth 15–16 cm
• 6–12 months — head circumference 45–46 cm; crown diameter 14.3 or 14.6 cm respectively; hat depth 16–17 cm
• 1–2 years — head circumference 47–48 cm; crown diameter 15.0 or 15.3 cm respectively; hat depth 16–17 cm
• 2–3 years — head circumference 49–50 cm; crown diameter 15.6 or 15.9 cm respectively; hat depth 17–18 cm
• 3–5 years — head circumference 51–54 cm; crown diameter 16.2, 16.6, 16.9, or 17.2 cm respectively; hat depth 18–20 cm
• Child over 5 years or adult woman — head circumference 55–57 cm; crown diameter 17.5, 17.8, or 18.2 cm respectively; hat depth 20–21 cm
• Adult man — head circumference 58–60 cm; crown diameter 18.5, 18.8, or 19.1 cm respectively; hat depth 21–23 cm

Use the chart as a starting point rather than a substitute for checking fit: yarn, stitch pattern, gauge, and the amount of ease can all affect the finished hat.