Homeโ€บConvertersโ€บEverydayโ€บHat Size Converter

Hat Size Converter

Everyday

Convert head circumference to US, UK, and metric hat sizes instantly. Enter your measurement in cm or inches and get the matching hat size for any brand.

Reviewed by the thecalcu.com team ยท Last updated July 27, 2026

From
To
All conversionsfor 1 Head Circumference (cm)
Head Circumference (cm)1
Head Circumference (in)0.39370079
US / UK Hat Size0.12531956

What is a Hat Size?

A Hat Size Converter translates a measured head circumference into the hat size used by a specific sizing system, US/UK numeric sizes, metric centimetres, or inches. Hat sizing causes confusion because different brands and regions label the same physical fit differently: a hat marked "58" in one store might be the same fit as a "7 1/4" in another, even though both are correct for the same head.

This converter removes that guesswork. Measure your head circumference once, enter it, and instantly see the equivalent size across every system, the same way the Shoe Size Converter and Clothing Size Converter handle sizing confusion for footwear and apparel.

Why Use a Hat Size Converter?

Buying a hat online from an international brand almost always means encountering an unfamiliar sizing system. A US-labelled hat uses a number like 7 1/8, a metric-labelled one uses centimetres like 57, and without a quick way to convert between them, shoppers either guess or order multiple sizes to be safe.

This converter solves that in one step: measure your head circumference with a tape measure, enter the number, and get the matching size for whichever system the hat you want uses. It's especially useful when ordering custom or fitted hats, like flat caps, fitted baseball caps, or formal hats, where an ill-fitting size can't simply be adjusted with a strap, unlike adjustable snapback styles.

Who Should Use This Converter?

  • Online shoppers buying hats, caps, or helmets from brands that use a sizing system different from what they're used to.
  • International travellers purchasing hats abroad where local sizing conventions differ from their home country.
  • Gift buyers who know a friend or family member's head circumference but need to convert it to the hat brand's labelled size.
  • Costume and uniform suppliers needing to fit hats to a measured head circumference for groups of people at once.
  • Anyone comparing measurements alongside the Length Converter when converting between metric and imperial units for any clothing or accessory purchase.

What Insights Does the Hat Size Converter Give You?

The converter gives you the same physical measurement expressed in whichever sizing system you need:

  • Head Circumference (cm), the metric measurement used by many international and European hat brands.
  • Head Circumference (in), the imperial measurement some US retailers list alongside the numeric hat size.
  • US / UK Hat Size, the traditional numeric size (such as 7 1/8 or 7 1/4) used by most American and British hatmakers.

Because all three values represent the exact same physical fit, you can confidently match your measurement to whichever sizing label a specific hat uses, without relying on a generic "S/M/L" guess.

How to use this Hat Size calculator

  1. Measure your head circumference with a soft tape measure, positioned about 1.5 cm above your eyebrows and ears.
  2. Select the unit you measured in from the From dropdown, Head Circumference (cm) or Head Circumference (in).
  3. Enter your measured value in the input field.
  4. Select US / UK Hat Size in the To dropdown to see your equivalent numeric hat size.
  5. Use the swap (โ‡…) button to convert in the opposite direction if you already know your hat size and want your head circumference.
  6. Round the result to the nearest standard size offered by the brand you're buying from.
Show formula & methodology โ†“Show less โ†‘

Formula & Methodology

Hat sizing converts directly from head circumference using these relationships:

US / UK Hat Size = Head Circumference (in) รท ฯ€

Head Circumference (cm) = US / UK Hat Size ร— ฯ€ ร— 2.54

Since 1 inch = 2.54 cm, the direct centimetre-to-size factor works out to approximately 7.9796 cm per size unit.

Worked example: For a measured head circumference of 58 cm:
- Convert to inches: 58 รท 2.54 โ‰ˆ 22.83 in
- Hat Size = 22.83 รท ฯ€ โ‰ˆ 7.27, rounded to the nearest standard size of 7 1/4

Frequently Asked Questions

What is a hat size converter?
A hat size converter translates your head circumference measurement into the hat size used by a particular brand or region, since US, UK, and metric hat sizing systems all use different numbers for the same physical fit. Enter your head circumference in centimetres or inches, and the converter instantly shows the matching US/UK hat size, so you can buy a hat online with confidence.
How do I measure my head circumference for hat sizing?
Wrap a soft tape measure around your head about 1.5 cm above your eyebrows and ears, at the widest point of your head, keeping the tape snug but not tight. Note the measurement in centimetres or inches and enter it into the converter to get your hat size.
What is the formula for converting head circumference to US hat size?
US and UK hat sizes are calculated by dividing the head circumference in inches by ฯ€ (approximately 3.1416). For example, a head circumference of 58 cm (22.83 inches) gives a hat size of roughly 22.83 รท 3.1416 โ‰ˆ 7.27, typically rounded to the nearest standard size like 7 1/4.
Are US and UK hat sizes the same?
Yes, US and UK hat sizes use the same numeric system, both derived from head circumference in inches divided by ฯ€. A size 7 1/4 hat fits the same head in both the US and UK, unlike clothing or shoe sizes which differ between the two countries.
Why do hat sizes look different between brands?
Some brands label hats with the numeric US/UK size (like 7 1/8), others use metric centimetres directly, and some use simplified S/M/L/XL labels. This converter handles the numeric and metric conversions so you can match your measured head circumference to whichever system a specific brand uses.
What is the difference between this and the Shoe Size Converter?
The [Shoe Size Converter](/shoe-size-converter/) converts foot length across India/UK, EU, and US sizing systems using a non-linear lookup table, since shoe sizing doesn't scale evenly. Hat sizing is more mathematically consistent, it scales directly with head circumference, so this converter uses a direct formula rather than a size chart.
How accurate is hat size from head circumference alone?
Head circumference is the primary factor in hat sizing and gives an accurate starting point for most adult head shapes. Hat fit can still vary slightly by brand and hat style, a fitted cap and a wide-brim hat from different brands may fit slightly differently even at the same labelled size.
What head circumference is considered an average adult size?
An average adult head circumference is roughly 56โ€“58 cm, which corresponds to a US/UK hat size of approximately 7 to 7 1/4. Children's head circumferences are typically smaller, ranging from about 48โ€“54 cm depending on age.
Can I convert hat size back to head circumference?
Yes, select US/UK Hat Size as the 'from' unit and Head Circumference (cm or in) as the 'to' unit. The converter works in both directions, so you can go from a known hat size back to the circumference it corresponds to.
Do I need to round my hat size to a standard size?
Most hat brands sell in standard increments like 7, 7 1/8, 7 1/4, and so on, so round your converted result to the nearest standard size your preferred brand offers. If your result falls between two standard sizes, sizing up slightly is usually more comfortable than sizing down.
Also known as
hat size charthead circumference to hat sizeUS hat size converterUK hat sizecap size converterhat size calculatorcm to hat sizeinches to hat sizebeanie size chart