Hat Size Guide: Centimeters, Inches, US and UK Sizes
Start with your measured head circumference. Converting between centimeters and inches is straightforward: the conversion itself is exact, although the inch values in the table are rounded for display. The US and UK numeric sizes are approximate common references, so for an actual purchase the current chart for the exact manufacturer, model or silhouette takes precedence.
If you do not yet have a reliable circumference, use How to Measure Your Head for a Hat. That guide explains how to measure; this one shows how to interpret the result.
Hat Size Conversion Chart
| Head circumference (cm) | Circumference (in) | Approx. common US fitted size | Approx. common UK size |
|---|---|---|---|
| 54 | 21.26 | 6¾ | 6⅝ |
| 55 | 21.65 | 6⅞ | 6¾ |
| 56 | 22.05 | 7 | 6⅞ |
| 57 | 22.44 | 7⅛ | 7 |
| 58 | 22.83 | 7¼ | 7⅛ |
| 59 | 23.23 | 7⅜ | 7¼ |
| 60 | 23.62 | 7½ | 7⅜ |
| 61 | 24.02 | 7⅝ | 7½ |
| 62 | 24.41 | 7¾ | 7⅝ |
| 63 | 24.80 | 7⅞ | 7¾ |
| 64 | 25.20 | 8 | 7⅞ |
| 65 | 25.59 | 8⅛ | 8 |
US and UK values are approximate common references, not universal brand assignments. Check the current chart for the exact manufacturer, model or silhouette before choosing a size.
The centimeter rows are reference points, and the inch values are calculated from them and rounded to two decimal places. The US and UK columns show common numeric-size equivalents, not guaranteed sizes for every brand.
How to Use This Guide
Start With Your Measured Circumference
Keep the measurement you actually obtained. Do not replace a value such as 58.4 cm with 58 or 59 simply because this table uses whole-centimeter reference rows. The decimal is useful information, especially when it falls between two chart entries.
NESH uses centimeters as the main reference measurement. If your measurement is in inches, it can be converted without changing the underlying circumference. This is different from translating that circumference into a brand's size label.
Treat Numeric Sizes as Approximate
A number such as US 7¼ or UK 7⅛ is a nominal size reference. It is not another direct measurement of your head, and it is not evidence that every hat carrying that label has identical internal dimensions.
Use the numeric columns to identify likely neighboring labels. Treat the result as provisional until you have checked the relevant manufacturer's current chart.
Check the Current Manufacturer Chart Before Buying
Manufacturers may round differently, group measurements into bands, use a centimeter value as the label, or publish separate charts for different silhouettes. A chart can also change. For those reasons, the current chart for the exact product family is the purchase reference—not a generic conversion table.
Current official charts from Stetson, Akubra and Lock & Co. illustrate both the broad pattern and the differences in presentation. Check the chart itself rather than assuming that a familiar label transfers unchanged between brands.
How Centimeters and Inches Convert
Centimeters and inches are units for the same circumference. The conversion is:
inches = centimeters ÷ 2.54
centimeters = inches × 2.54
The relationship is exact because one inch is defined as 2.54 centimeters. The table displays calculated inches to two decimal places, so the visible number is rounded for readability. NIST's SI guidance provides the measurement basis for that conversion.
A manufacturer may round differently or show a convenient fractional-inch value in its own chart. That's fine—when you're buying that brand, follow its published chart rather than trying to recalculate the label yourself.
How Common US Fitted Sizes Work
Common US fitted hat sizes traditionally approximate the head's diameter in inches:
circumference in inches ÷ π
The resulting nominal sizes are commonly expressed in one-eighth steps. Levine Hat Co., a specialist hat retailer, directly describes this traditional convention. Its explanation is useful support for the method, but it is not a legal or universal sizing standard.
For a 58 cm reference, the calculation is approximately 58 ÷ 2.54 ÷ π = 7.27. The nearby common one-eighth label is 7¼, which is the approximate reference shown in the table. This arithmetic explains the convention, but manufacturers may use bands, different rounding, or silhouette-specific assignments. Use the current chart for the product you are considering.
How Common UK Hat Sizes Compare
In the compared ranges published by Akubra and Lock & Co., the common UK label is one eighth below the corresponding common US label. At the 58 cm reference row, for example, the table shows approximately US 7¼ and UK 7⅛.
That one-eighth relationship is an approximate reference supported by the compared source range, not a universal international standard. Use the manufacturer's own column when one is published.
Why S, M, L and XL Are Not Universal
We leave letter sizes out of the main table because their measurement ranges vary by brand, product and silhouette. One manufacturer may group two centimeter values under M, another may publish a single anchor value, and a stretch-size range may overlap the neighboring label. Some products are sold as one size even when the same brand uses several letter sizes elsewhere.
A universal XS/S/M/L/XL column would conceal those differences and create a precision the evidence does not support. Treat a letter label as part of the exact product's sizing system, then read its stated circumference range.
The same caution applies to “EU size.” Many charts use centimeters directly as the size label. A metric or centimeter label does not, by itself, establish a separately standardized universal EU hat-size system.
What to Do When Your Measurement Falls Between Reference Rows
Keep the original measurement and inspect both adjacent reference rows. Do not silently force the value into one row.
For example, 58.4 cm lies between the 58 and 59 cm rows. It is approximately 22.99 inches, but this guide does not turn that result into a purchase size. The adjacent rows provide context; the exact manufacturer's current chart determines how that product handles the measurement.
The reverse conversion works the same way: 23 inches equals 58.42 cm, or 58.4 cm when displayed to one decimal place. It still lies between the 58 and 59 cm rows, so keep the calculated value and consult both neighboring references.
There is no universal instruction to size up, size down or choose the nearest generic row. Some named brands give their own between-size instructions, but those rules belong to those brands and products. They do not become a general NESH rule.
Conversion Is Not the Same as Fit
The chart translates circumference into reference labels. It does not determine how a particular hat will distribute pressure, where its crown will sit, or whether its proportions will feel comfortable.
Head Shape
Two people can have the same circumference and experience the same hat differently because their head shapes distribute that circumference differently. A nominal size cannot establish whether a head is relatively round, oval or long oval, and it cannot predict pressure points by itself.
Use Head Shapes for Hats for the next layer. The NESH Hat Size + Head Shape Profiler can also accept circumference in centimeters or inches, convert between those units, and continue into optional self-observed head-shape guidance.
Model- and Silhouette-Specific Evidence
Crown depth, internal construction, material, adjustability and silhouette can change how a labeled size behaves. Even within one manufacturer, separate silhouettes may use different charts or fit differently. A matching nominal number therefore does not prove model compatibility.
Model-specific conclusions require evidence about that model. If NESH has not published that evidence, the absence should be treated as unknown—not as proof that the model is unsuitable. See NESH Fit Intelligence Methodology for how we decide what a source actually supports—and what we won't claim without enough evidence.
Continue Through NESH FIT
The useful sequence is straightforward:
MEASURE → CONVERT → UNDERSTAND HEAD SHAPE → ASSESS MODEL-SPECIFIC EVIDENCE
If you already have a circumference, enter it into the NESH Hat Size + Head Shape Profiler to convert between centimeters and inches and continue into optional head-shape guidance. It is a measurement tool, not a product-size or model recommendation.
For the broader system, continue to FIT hub. Keep your original head measurement, use the conversions as a guide, and make the final size choice from the current chart and fit information for the hat you're actually buying.