Hat Size Calculator

Calculate your hat size from head circumference. Converts between US, UK, EU, and metric sizing for fitted caps, beanies, and helmets.

Hat Size Calculator

Around forehead, 1 inch above ears
cm
US Size
7⅛
Standard fit
UK Size
7
UK runs ⅛ smaller than US
EU Size
57
57.0 cm circumference
Generic Size
M
S/M/L/XL for adjustable hats
Head Circ.
57.0 cm
22.44 inches
Type Advice
Fitted caps need exact sizing — no adjustment.
Selected: fitted-cap

Complete Size Chart

USUKEU (cm)GenericRange (cm)
6⅝53XS5253.5
6⅝54S53.554.5
6⅞55S54.555.5
76⅞56M55.556.5
7⅛757M56.557.5
7⅛58L57.558.5
7⅜59L58.559.5
7⅜60XL59.560.5
7⅝61XL60.561.5
7⅝62XXL61.562.5
7⅞63XXL62.564
87⅞64XXXL6466

Fit Comparison by Type

Fitted CapExactTolerance: NoneMust match precisely
SnapbackAdjustableTolerance: ±2 sizesCovers a range
FlexfitStretchTolerance: ±1 sizeS/M or L/XL ranges
BeanieStretchTolerance: ±2 sizesOne-size fits most
FedoraExactTolerance: NoneBuy exact; can steam-stretch felt
Bike HelmetPaddedTolerance: ±1 cmInternal pads fine-tune

Head Shape Visual

XS
<54 cm
S
54-55 cm
M
56-57 cm
L
58-59 cm
XL
60-61 cm
XXL
62+ cm
Planning notes, formulas, and examples

About the Hat Size Calculator

Whether you're ordering a fitted cap online, choosing a hard hat for work, or picking out a fedora, knowing your hat size is essential. This hat size calculator converts your head circumference measurement into US, UK, EU, and generic (S/M/L) sizing, with specific guidance for different hat types.

Hat sizing varies by system: US sizes use fractional numbers (6⅞, 7¼), UK sizes are nearly identical to US, EU sizes use centimeters, and many casual hats use simple S/M/L/XL designations. Each system refers to the same head circumference but uses different notation, which makes online shopping confusing.

This calculator goes beyond basic conversion. It accounts for hat type — a snug beanie fits differently than a structured baseball cap or a safety helmet with internal suspension. Material matters too: straw hats may stretch, felt can be steamed to shape, and synthetic caps have fixed sizing. The tool shows your measurements mapped across all systems with type-specific recommendations and notes on adjusting for hair volume.

When This Page Helps

Buying hats online is mostly a sizing-translation problem. This calculator turns one head measurement into the US, UK, EU, and generic labels that different brands actually use.

It is useful because fitted caps, casual hats, and helmets all present size information differently even when they are built around the same circumference. Keeping those systems aligned in one place reduces ordering mistakes.

How to Use the Inputs

  1. Measure your head circumference about 1 inch above your ears, across your forehead.
  2. Use a soft measuring tape or a string you can then measure flat.
  3. Enter the measurement in inches or centimeters.
  4. Select the hat type for fit-specific guidance.
  5. View your size in US, UK, EU, and generic S/M/L formats.
  6. Check the full size chart to find your range.
  7. Review material stretch notes for your hat type.
Formula used
US Size = circumference (inches) ÷ π ≈ circumference ÷ 3.14. EU Size = circumference in cm. Generic: <54cm = XS, 54–55 = S, 55–57 = M, 57–59 = L, 59–61 = XL, 61+ = XXL.

Example Calculation

Result: US 7⅛ / UK 6⅞ / EU 57

22.5 inches = 57.15 cm. US fitted size ≈ 22.5 ÷ 3.14 = 7.16 → rounds to 7⅛. EU size rounds to 57. Generic sizing = Medium.

Tips & Best Practices

  • Measure mid-forehead — not on the hairline or at the crown.
  • If using a string, mark it and lay flat against a ruler.
  • Thick hair? Measure over it as you'd normally wear a hat.
  • Helmets should be snug — size for safety, not comfort.
  • Felt hats can be steamed to stretch ¼–½ size if slightly small.
  • Order fitted hats ⅛ size up if you plan to wear liners in winter.

Hat Sizing Systems

The US system divides circumference by pi to get a fractional number (6¾ through 8). The UK system is nearly the same but ⅛ smaller for each size. EU/metric sizing simply uses head circumference in centimeters. Generic S/M/L sizing covers wider ranges and is less precise but works for adjustable or stretchy hats.

Hat Types and Fit Differences

Fitted baseball caps need the most accurate sizing because there's no adjustment. Snapbacks and flexfit caps cover ranges (e.g., S/M or L/XL). Beanies are the most forgiving, stretching to accommodate different head sizes. Cowboy hats and fedoras typically use the US sizing system with ⅛ increments.

Safety Headwear

Bike helmets, hard hats, and motorcycle helmets have their own sizing standards. Always follow the manufacturer's size chart and measure as directed. Safety helmets should be snug without pressure points, and most have internal adjustment systems for fine-tuning fit.

Sources & Methodology

Last updated:

Frequently Asked Questions

  • Wrap a soft tape measure around your head about 1 inch above your ears and eyebrows, across the widest part of the back of your head. Keep the tape snug but not tight. This is your head circumference.