# Hat Size Calculator

> Calculate your standard US hat size from your head circumference.

Page: https://askcalculators.com/calculator/hat-size-calculator/
Definition: https://askcalculators.com/calculator/hat-size-calculator/definition.json
JSON Schema: https://askcalculators.com/calculator/hat-size-calculator/schema.json
Version: 7.0.0
Maintained by: AskCalculators (software project; not a credentialed reviewer)
Qualified review: pending. Automated checks do not establish professional approval.
Page status: Live
Review status: Pending

## Use
Open the calculator page and enter values. Query-string parameters can restore and bookmark a calculation.
Example: https://askcalculators.com/calculator/hat-size-calculator/?circumference=58

## Inputs
- circumference: Head Circumference (cm); type=number; optional; default=58

## Outputs
- result: Result; format=text; primary

## Formula
Head circumference is mapped to the nearest published hat size range.

## Rules
- Empty optional inputs are undefined, not zero.
- Hidden conditional inputs are ignored.
- Do not invent missing required inputs.

Notice: Sizing charts differ by brand and region; compare the result with the seller or manufacturer chart.