Hat Size Conversion Chart: Every System Side by Side
Four systems describe the same head and none of them agree on notation. We'll put them in one table.
Every hat sizing system reduces to head circumference, so converting is a matter of finding your measurement in centimeters and reading across. US fitted uses diameter-derived fractions, UK fitted runs one eighth smaller, European and Japanese sizing use centimeters directly, and alpha sizing groups everything into two or three bands. Work in centimeters and the conversions stop being confusing.
- Centimeters are the common currency. Convert through the measurement.
- UK fitted runs 1/8 smaller than US. Same head, different number.
- European and Japanese sizing are the measurement. Their numbers are the head circumference itself, not a code.
- Made in the USA, no minimums. One hat is a real order.
The Conversion Chart
| Inches | cm / EU / JP | US fitted | UK fitted | Alpha |
|---|---|---|---|---|
| 21 1/4 | 54 | 6 3/4 | 6 5/8 | S |
| 21 5/8 | 55 | 6 7/8 | 6 3/4 | S |
| 22 | 56 | 7 | 6 7/8 | S / M |
| 22 3/8 | 57 | 7 1/8 | 7 | M |
| 22 3/4 | 58 | 7 1/4 | 7 1/8 | M / L |
| 23 1/8 | 59 | 7 3/8 | 7 1/4 | L |
| 23 1/2 | 60 | 7 1/2 | 7 3/8 | L |
| 23 7/8 | 61 | 7 5/8 | 7 1/2 | L / XL |
| 24 1/4 | 62 | 7 3/4 | 7 5/8 | XL |
| 24 5/8 | 63 | 7 7/8 | 7 3/4 | XL / XXL |
| 25 | 64 | 8 | 7 7/8 | XXL |
European and Japanese sizes are simply the centimeter measurement, which makes them the clearest system.
Our system-specific charts are at the baseball cap size chart and the Flexfit hat size chart.
When ordering from a non-US supplier, work in centimeters. Converting through fitted numbers introduces the UK offset and brand variation at the same time.
The Math Behind US Fitted
US fitted numbers look arbitrary because they derive from head diameter rather than circumference.
Divide a circumference by pi and you get roughly the size. A 22-inch head is about 7 inches across, which is a size 7. A 23 1/2 inch head is about 7 1/2 inches across, hence 7 1/2.
Sizes advance in eighths, which is roughly three eighths of an inch of circumference per step. Knowing the relationship means you can convert without a chart and sanity-check a size that seems wrong.
Our detail is at the fitted hat size chart.
Why UK Sizes Run Smaller
UK fitted sizing uses the same fractional notation and a slightly different derivation, which puts it one eighth below US for the same head.
A US 7 1/4 is a UK 7 1/8. A US 7 is a UK 6 7/8. The head has not changed; the label has.
That single eighth is enough to matter, since it is a full size step. Anyone ordering British-made headwear from a US measurement and reading the number directly will get a hat a size too small.
The reliable approach is to convert through centimeters, which both systems agree on.
UK fitted sizes run one eighth smaller than US for the same head. Reading a US size number directly on a British-made hat produces a cap a full size too small.
Alpha Sizing Is the Loosest
Small, medium, large and XL are the vaguest system and the most common on stretch-fit and knit products.
The problem is that alpha bands are not standardized. One manufacturer's L/XL covers 22.5 to 24 inches; another's covers 23 to 24.5. Two hats both labeled large can differ by a full inch of coverage.
Three practical points. Always check the manufacturer's actual range rather than assuming the letter means anything. Expect alpha bands to overlap, which is intentional on stretch products. And for anyone falling between two bands, alpha sizing is the worst system to be ordering in.
Our note on the youth hat size chart covers the children's ranges, where alpha naming varies even more.
- Reading UK fitted numbers as US. They run a full size apart.
- Assuming alpha sizes are standardized. Bands differ between manufacturers.
- Converting through fitted rather than centimeters. It compounds two variables.
- Ignoring sweatband thickness. It moves fit at any labeled size.
Converting Between Constructions
The other conversion people need, and it works differently from unit conversion.
- Fitted to adjustable. Any fitted size between about 6 3/4 and 7 3/4 sits inside a standard adjustable cap's range, so an adjustable cap covers it directly.
- Fitted to stretch-fit. Sizes up to about 7 1/8 fall in S/M; 7 1/8 through 7 5/8 in L/XL; above that in XXL. The boundaries overlap, and anyone at a boundary should size up.
- Adjustable to fitted. Requires an actual measurement, since the adjustable cap tells you nothing about the head inside it beyond a two and a half inch range.
That last point catches people out. Knowing you wear an adjustable cap does not tell you your fitted size, and guessing produces a wasted hat.
Wearing an adjustable cap tells you nothing precise about your fitted size, since one adjustable size covers two and a half inches. Measure before ordering fitted.
Youth and Children's Conversions
Children's sizing converts less cleanly than adult, because the naming is not standardized at all.
Adult systems at least agree on the underlying measurement. Children's ranges do not agree on what the names cover — one manufacturer's toddler is another's youth XS, some skip bands entirely, and alpha naming for children varies more than for adults.
Rough equivalences that hold across most brands:
- Infant — 41 to 47 cm / 16 to 18.5 in
- Toddler — 47 to 51 cm / 18.5 to 20 in
- Youth XS — 48 to 51 cm / 19 to 20 in
- Youth small — 51 to 53 cm / 20 to 21 in
- Youth large — 55 to 57 cm / 21.5 to 22.5 in
The overlap between toddler and youth XS is real rather than chart imprecision — they describe nearly the same circumference in different proportions.
For children's programs the practical approach is the same as for international ordering: work in centimeters, check the specific manufacturer's chart, and choose adjustable closures so the conversion matters less.
Where Charts Stop Being Reliable
- Sweatband thickness. A padded band takes up internal circumference, so the same labeled size fits smaller.
- Crown depth. A deeper crown sits further down and feels looser at the same measurement.
- Hair. Volume adds effective circumference that no chart accounts for.
- Fabric give. Wool blends yield under tension; stiff cotton does not.
- Shrinkage. Cotton moves permanently in heat, which on a fitted cap changes the size.
Charts get you to the right band. The construction decides whether the hat is comfortable inside it.
What We Tell Customers Who Ask
Adjustable caps sidestep conversion entirely, which is worth something on any program shipping internationally or ordering from multiple suppliers.
If you know your size in one brand, check the chart before assuming it transfers. Sweatband and crown differences move fit even within the same country's system.
For programs mixing suppliers, specify measurements in centimeters on every order. It is the one figure every system agrees on and it removes a whole class of error.
For anything international or multi-supplier we would order adjustable caps and specify ranges in centimeters. For fitted, take an actual measurement rather than converting from a known adjustable size.
We work from centimeters when a customer is converting between systems, because it is the only figure that does not carry a hidden offset. Free digital proof, free artwork setup on twelve or more, no minimums.
The baseball cap size chart, the fitted hat size chart, the Flexfit hat size chart.
Frequently Asked Questions
How do I convert hat sizes?
Convert through head circumference in centimeters, which every system agrees on. European and Japanese sizes are the centimeter measurement directly, and US and UK fitted sizes read across from it.
Are UK and US hat sizes the same?
No. UK fitted sizes run one eighth smaller than US for the same head, so a US 7 1/4 is a UK 7 1/8. That is a full size step and reading the number directly gets it wrong.
What is a size 7 hat in centimeters?
About 56 centimeters, or 22 inches of head circumference. US fitted numbers derive from head diameter, so 7 means roughly 7 inches across.
Are small, medium and large standardized?
No. Alpha bands differ between manufacturers, so two hats both labeled large can cover ranges an inch apart. Always check the actual range rather than the letter.
Can I work out my fitted size from my adjustable cap?
Not precisely. One adjustable size covers about two and a half inches, so it tells you very little about the head inside it. Measure before ordering fitted.
Why do European sizes look simpler?
Because they are the measurement. A European 57 is a 57 centimeter head, with no derivation or offset involved, which makes it the clearest of the systems.
Is there a minimum order?
No. One hat is a real order, and artwork setup is free on orders of twelve or more.
Convert through centimeters and it all lines up. Order custom hats — start on the quick order page — fitted, stretch-fit and adjustable in every system. Free digital proof before production, free artwork setup on twelve or more, no minimums. Browse custom hats.
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