Hat Size Converter Free Online
Convert hat sizes between US, UK, EU (centimeters), and head circumference in millimeters. Useful for caps, fedoras, helmets, and online hat shopping.
All Systems
Pro — bulk batch conversion, API access, history & favorites
API access · Priority queue · Team workspace
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How It Works
Pick Your System or Ingredient
Choose your home size system, ingredient, or input mode using the dropdowns and category buttons. Defaults are sensible so you can start typing immediately.
Enter or Pick a Value
Type a number, choose a size, or use the dual inputs (e.g. ft + in or min + sec). Conversion runs as you type — no Convert button.
See Every Equivalent
Below the main result, the All Conversions panel shows your value across every supported system or unit at once — perfect for international shopping or recipe scaling.
Hat Size Converter Features
Head Circumference
Hat sizes are based on head circumference in mm. Wrap a tape measure around the widest part of your head, just above your eyebrows.
4 Systems
US (1/8 inch fractions), UK (1/8 inch slightly smaller), EU (cm), mm circumference. EU is the easiest because it directly matches the measurement.
Caps & Fedoras
Works for fitted baseball caps, fedoras, top hats, and helmets. Stretch caps (one-size-fits-most) are not standardized.
Online Ready
Buy a fedora from Italy or a fitted cap from the US — convert your size in either direction and order with confidence.
Live Conversion
Pick a system, see the equivalent in every other system instantly.
100% Private
Pure client-side lookup. No data leaves your browser.
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| Full hat size conversion | ||
| Live conversion | ||
| All-systems result panel | ||
| Bulk CSV / Excel conversion | — | |
| REST API access | — | |
| Custom precision settings | — |
Frequently Asked Questions
Use a soft tape measure around the widest part of your head — about 1 cm above your eyebrows and ears. Keep the tape level and snug but not tight. Measure twice and average. That number in mm is your direct EU/cm hat size.
Almost. US hat sizes are based on head circumference in 1/8 inch fractions (e.g. US 7 = 22 inch). UK uses the same fractions but rounded slightly differently — UK 7 ≈ US 7 1/8. Use the chart for exact matches.
EU hat sizes equal head circumference in centimeters (e.g. 56 cm = EU 56). It is the simplest and most precise system because there is no conversion involved.
Men: 22 7/8 inch ≈ 58 cm ≈ US 7 1/4. Women: 22 inch ≈ 56 cm ≈ US 7. About 95% of adults fall between 54 and 62 cm.
Both. New Era 59FIFTY and other "fitted" caps follow this size chart. Adjustable snapbacks and dad hats fit a range of head sizes via Velcro/snap closure.