Hat Size Calculator — Cast On & Dimensions from Head Size
Calculate cast-on stitches, hat height, and crown decrease schedule from head circumference.
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.