Hat Knitting Calculator (Beanie Cast-On, Rounds & Crown Decreases)
Plan a knitted beanie from head circumference and gauge: stitches to cast on with negative ease, rounds to knit before the crown and the crown decreases, rounded to fit your rib and sections.
How it works
cast-on = head × (1 − ease) × stitches per cm, rounded to a multiple of LCM(rib repeat, sections) · stitches per section = cast-on ÷ sections · decrease rounds = stitches per section − 1 · crown rounds = 2 × decrease rounds − 1 · crown depth = crown rounds ÷ rounds per cm · rounds before crown = (hat height − crown depth) × rounds per cm
A beanie is a tube knit slightly smaller than the head (negative ease, usually about 10%) and closed with a crown that decreases one stitch per section every other round until only one stitch per section is left. The cast-on is rounded so it divides by both the rib repeat and the number of crown sections. Crown depth depends on your row gauge, so the calculator subtracts it from the total height to tell you how long to knit straight. Craft Yarn Council head-size charts give about 53–56 cm (21–22 in) for adults and 20–23 cm (8–9 in) hat height.
Worked example
For a 56 cm head at 22 stitches and 30 rounds per 10 cm with 10% negative ease: 56 × 0.9 × 2.2 = 110.9, rounded to a multiple of 8 (1×1 rib, 8 sections) = 112 stitches, about 50.9 cm around. Each section has 14 stitches, so there are 13 decrease rounds and 25 crown rounds (8.3 cm). For a 21 cm hat knit 38 rounds (12.7 cm) before starting the crown, and cinch the last 8 stitches closed.
Sources: Craft Yarn Council — Head circumference and hat sizing · Craft Yarn Council — Gauge
Frequently asked questions
How many stitches do I cast on for a hat?
Multiply your head circumference by about 0.9 (10% negative ease) and by your stitches per cm or inch, then round to a number your rib and crown sections divide into. With worsted yarn at 20 stitches per 10 cm a 56 cm adult hat needs about 100 stitches.
How much negative ease should a beanie have?
Usually 5–15%. Stretchy ribbed hats work well at 10–15%, hats in colourwork or cables that do not stretch much need only 5% or so.
How long should I knit before the crown decreases?
Total hat height minus the crown depth. An adult beanie is about 20–23 cm (8–9 in) tall, and an 8-section crown decreased every other round is usually 7–9 cm deep.
Why decrease every other round?
It gives a rounded crown that matches the curve of the head. Decreasing every round makes a flat, wide top; you can switch to every round for the last few rounds if you want a flatter finish.
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This calculator is for educational purposes. Double-check important results before acting on them.