Hat Size Calculator

How to measure your head for a hat

You need a soft tape measure. If you don't have one, a piece of string and a ruler will do.

1. Place the tape about 1 inch (2.5 cm) above your eyebrows and ears, where the band of a hat sits.
2. Wrap it around the widest part of the back of your head.
3. Keep it level and snug, not tight. You should be able to slide a finger under it.
4. Read the measurement where the tape overlaps. Measure two or three times and use the largest.

Measure with your hair the way you'll wear it under the hat. Thick hair, braids or a bun change the number. Our step-by-step guide on how to measure your head for a hat has photos.

Hat size chart

This is the chart the calculator uses, matching our full hat size chart:

Letter sizes vary more than fitted sizes. One brand's Medium covers 57 to 58 cm, another's 56 to 58. When a brand lists centimetres, trust those.

Where hat sizes come from

US and UK fitted hat sizes come from the hat-making trade. A hat size is roughly the diameter of the head in inches, which is why you get it by dividing the circumference by pi (about 3.14). Sizes go up in eighths of an inch. The UK scale uses the same idea with a slightly different starting point, so UK sizes sit one eighth below US sizes for the same head.

European sizes skipped all that and simply use the head circumference in centimetres: a 57 cm head wears a size 57. That makes EU sizes the easiest to check: measure, and buy the number you get.

Hat sizes by type of hat

Different hats handle size in different ways:

Our guides on the best hats for round faces and oval faces cover style, and the size guide for hat brands covers how makers chart sizes.

Head shape matters too

Two heads with the same circumference can need different hats. Heads range from round oval (nearly as wide as they are long) to long oval (much longer front to back than side to side). Most hats are made for an intermediate oval.

If a hat in your size presses on your forehead and the back of your head but feels loose at the sides, your head is probably a long oval. If it presses at the sides, a rounder oval. Felt hats can often be shaped by a hatter to fit; caps and straw hats usually can't. Helmets work the same way; see what 65 cm means in helmet sizing if you have a large head.

Between sizes?

• Size up and add hat sizing tape inside the sweatband. It's cheap, invisible and adjustable.
• For felt hats, a hatter can stretch a hat up by a small amount.
• For beanies and caps, stretch and adjustable straps cover most in-between sizes.

Hat sizes for children

Children's heads grow quickly, especially in the first few years, so measure before every purchase. Many children's hats are sold by age, but age is a rough guide; head circumference is better. If you're buying a hat for a newborn or baby, choose soft, stretchy fabrics and avoid anything tight.

Common mistakes

• Measuring too low, across the eyebrows. The tape should sit where the hat band will.
• Pulling the tape tight. Snug, not tight.
• Using your clothing size. "I'm a Large in shirts" says nothing about your head.
• Ignoring hair. Measure with your usual hairstyle.
• Confusing UK and US fitted sizes. They differ by an eighth.

Converting hat sizes

If you know one size, you can work out the others:

• US to UK: subtract ⅛. A US 7⅜ is a UK 7¼.
• US to cm: multiply by about 3.14 to get inches, then by 2.54. A US 7¼ is about 57.9, so a 58.
• cm to US: divide by 2.54, then by about 3.14, and round to the nearest eighth.

Or just use the calculator above. Our explainer on what a 58 band means in hats and the US to EU hat size conversion go further.

Worked examples

• A 57.5 cm head buying a fitted cap. Between 57 (7⅛) and 58 (7¼), the calculator rounds up to 7¼. If it's a little loose, a strip of sizing tape takes up the gap.
• A 22-inch head buying a European felt hat. 22 inches is 55.9 cm, so a European size 56, which is a US 7 and a UK 6⅞.
• A 61 cm head buying a beanie. Many one-size beanies stretch to about 60 or 61 cm, which is right at the edge. Look for an L/XL beanie or a brand that lists a range above 61 cm.
• Buying a hat as a gift. If you can't measure, a snapback or a knit hat is the safest choice; fitted hats are the riskiest.

Baby and children's hat sizes

Children's heads grow fastest in the first two years. These approximate head circumferences come from the WHO Child Growth Standards (median values, boys and girls combined, rounded); individual children vary a lot, so measure when you can.

Most children reach adult hat sizes in their teens. For babies, choose soft, stretchy hats that don't leave a mark on the forehead.

Adjusting a hat that's almost right

• Too loose: add hat sizing tape (a foam strip) behind the sweatband. It's cheap, removable and invisible.
• Slightly tight, felt hat: a hatter can stretch it with steam and a hat jack, usually by a small amount. Don't try this with straw, which can crack.
• Slightly tight, cap: fitted caps rarely stretch much; an adjustable cap is a better choice.
• Shape wrong: if a felt hat presses at the front and back but is loose at the sides, a hatter can reshape the crown to your head.

How a hat should fit

Put the hat on the way you'll wear it, then check:

1. It sits level, about an inch above your eyebrows and just above your ears, not perched on top or pulled down over your ears.
2. It's snug all the way round without pressure points. You should be able to slide a finger between the band and your forehead.
3. It doesn't move in a light breeze. Turn your head quickly; a well-fitting hat stays put.
4. No red line. After 15 minutes, a hat that leaves a deep mark or a headache is too small.
5. The brim sits evenly. If the front lifts or the back digs in, the shape is wrong for your head, not just the size.

Fitted caps explained

Fitted baseball caps, the ones with no strap at the back, use the same eighth-inch sizes as dress hats: 7, 7⅛, 7¼ and so on. They have very little give, so being an eighth out makes a real difference. If you're between sizes in a fitted cap, the larger size with a strip of sizing tape is usually more comfortable than the smaller one. Fitted caps can shrink slightly if washed hot, so spot-clean them instead. If you're buying for someone else, a "flex-fit" cap with an elastic band, sold in S/M and L/XL, is a safer choice than a true fitted size.

If you sell hats online

Shoppers rarely know their hat size, so they guess from their clothing size, and hats come back. On your product pages:

• Show head circumference in cm and inches for every size.
• Say whether the hat is fitted or adjustable, and the adjustable range.
• Explain how to measure, with a diagram.
• Note the fabric, since knits stretch and straw doesn't.

Tailor Size Guide adds a hat size chart to every product page, so shoppers can check before they buy.

Frequently asked questions

Sources and standards

1. WHO Child Growth Standards: head circumference-for-ageSource for the approximate median head circumferences of babies and young children.
2. Hat-making trade sizing conventionsUS and UK fitted hat sizes approximate head diameter in inches (circumference divided by pi), stepping in eighths; UK sizes sit one eighth below US.
3. European hat sizingEU hat sizes use head circumference in centimetres.
4. Tailor Size Guide hat size chartThe conversion table the calculator uses.