Hat Size Calculator — Cast On & Dimensions from Head Size
Calculate cast-on stitches, hat height, and crown decrease schedule from head circumference.
Measurement around the head above the ears
Stitches per 10cm from your gauge swatch
How snug the hat fits
How We Calculate This
This calculator uses head circumference and gauge to determine the cast-on count and crown shaping for a basic hat.
The formula
Cast on = (Head circumference - Ease) x (Stitch gauge / 10)
Hat height = Head circumference x 0.4 (approximately)
Frequently Asked Questions
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Last updated: February 2026
All calculations are estimates based on standard yarn weights and gauge. Results may vary with individual tension, yarn brand, and needle size.