Measure the widest part of your head — around the forehead, just above the ears and eyebrows, level all the way round — and use that number in centimetres. Most adult heads land between 54 and 60 cm. That single measurement is the only one that matters for a sauna hat, and it takes about fifteen seconds with a piece of string.
Sauna hats are more forgiving than baseball caps, because a felt hat has no fixed structure and the brim can be rolled. But "one size fits all" hides a real range, and it is worth knowing where you sit inside it before you order.
How to measure your head for a sauna hat
- Use a soft tape measure, or a piece of string you then hold against a ruler. A metal tape will not sit flat against your skull.
- Wrap it around the widest part of your head: about 1 cm above your eyebrows at the front, above the tops of your ears at the sides, and around the bulge at the back of your skull.
- Keep it level. The most common error is letting the tape ride up at the back, which under-measures by a centimetre or more.
- Snug, not tight. You should be able to slide one finger under the tape. Pull it tight and you will size down into a hat that leaves a mark on your forehead.
- Measure twice. If the two numbers differ, take the larger one — felt gives a little, but not much, and a hat that is slightly loose still works.
Do it with your hair the way you normally wear it in a sauna. If you tie long hair up under the hat, measure with it up.
What is a normal head size?
Most adults are closer to the middle than they expect. The US Army's ANSUR II anthropometric survey, one of the larger modern datasets, puts mean adult head circumference at roughly 57 cm for men and 55 cm for women, with the bulk of the population inside about 53–61 cm.
In practice that means a hat covering 55–61 cm reaches most adults, misses a portion of smaller heads, and misses the largest heads entirely. We would rather say that than pretend one size covers everybody.
| Head circumference | Inches | US hat size | Common label |
|---|---|---|---|
| 54 cm | 21¼" | 6¾ | Small |
| 55 cm | 21⅝" | 6⅞ | Small |
| 56 cm | 22" | 7 | Medium |
| 57 cm | 22½" | 7⅛ | Medium |
| 58 cm | 22⅞" | 7¼ | Large |
| 59 cm | 23¼" | 7⅜ | Large |
| 60 cm | 23⅝" | 7½ | X-Large |
| 61 cm | 24" | 7⅝ | X-Large |
US hat sizes are simply your head circumference in inches divided by pi — the diameter of a circle with that circumference. UK sizes run one-eighth smaller than US for the same head.
What does "one size" mean on a sauna hat?
It means the hat has a stated range and no closure. Ours is 55–61 cm. Others on the market state 54–62 cm, and some state nothing at all — which is the listing to be careful with.
The reason a single size can cover six or seven centimetres is that pressed felt has no seam, no lining and no band. It is one continuous piece with a small amount of give, and the brim does the rest of the work.
How the brim changes the fit
The brim is the adjustment mechanism, and most people never use it.
Rolled up: the hat sits higher and shorter on the head. This is the setting for a smaller head, or for a bather who wants their ears free.
Rolled down: the hat sits lower, covers the ear tops and the nape, and effectively adds one to two centimetres of coverage. Ears are thin, exposed and highly vascular — they are usually the first part of you that starts to hurt on a high bench — so most people end up here.
Rolling the brim down also tightens the fit slightly, because you are adding a doubled layer of felt around the circumference. If your hat feels a touch loose, roll it down before deciding it is too big.
What if you are outside the range?
Under 55 cm: the hat will fit but sit lower than intended. Roll the brim up one or two turns and it will be fine. Below about 52 cm — which includes most children — it will slide, and we do not currently make a child size.
Over 61 cm: do not force it. A felt hat stretched beyond its range sits on the crown of your head instead of around it, and it will not stay on when you lean forward. Look for a hat that states a larger range rather than assuming felt will give.
One thing that does not work as a fix: deliberately shrinking a hat that is too big. Wool felt shrinks in one direction and never comes back, and controlling how much is not realistic at home.
Does a sauna hat shrink?
Only if you make it. Felting is what happens when wool meets heat, moisture and mechanical agitation together — all three at once. That is precisely how the hat was made in the first place, and the process does not stop just because it is finished.
Sauna use itself supplies heat and moisture but not agitation, so a hat that lives in the sauna and dries flat holds its size. A hat that goes through a washing machine, or gets scrubbed and wrung out, will shrink and will not recover.
Wash in cool water, press the water out between your palms or in a towel, reshape it while damp, and air-dry it flat away from the stove.
How should a sauna hat fit?
It should sit on your head without pressure and stay put when you tilt forward. It should cover the tops of your ears when the brim is down. It should not leave a red line across your forehead, and it should not need to be held on.
Slightly loose is better than slightly tight. A sauna hat is not a fitted garment — its job is to hold a layer of still air around the hottest part of you, and it does that just as well with a little room.
Frequently asked questions
How do I measure my head for a sauna hat?
Wrap a soft tape measure around the widest part of your head — about 1 cm above your eyebrows, above your ears, and around the bulge at the back — keeping it level and snug but not tight. Record the number in centimetres. Measure twice and use the larger figure.
What size sauna hat should I get?
Match your head circumference to the hat's stated range. Most adults are 54–60 cm; the mean is around 57 cm for men and 55 cm for women. If a listing gives no range at all, treat that as a reason to look elsewhere.
Does one size really fit all in sauna hats?
No. "One size" means one stated range, usually somewhere between 54 and 62 cm. It reaches most adults but not the smallest or largest heads, and it does not fit children.
Will my sauna hat shrink in the sauna?
No. Felting needs heat, moisture and agitation together. A sauna supplies the first two; without rubbing or machine washing, the hat holds its size. Washing is the real risk, and it is avoidable.
Should a sauna hat be tight?
No. It should sit without pressure and stay on when you lean forward. A tight hat leaves a mark on your forehead and does not insulate any better — the insulation is the still air held in the felt, not the contact with your scalp.
What is 57 cm in hat size?
57 cm is about 22½ inches, which is a US hat size 7⅛ and a UK 7. US hat sizes are your head circumference in inches divided by pi.
Can kids wear a sauna hat?
Children need a smaller hat than the adult one-size range covers — most children measure below 52 cm and an adult hat will slide off. We do not currently make a child size.
Written by Angel Fuentes, Founder of Saunatär. We make seamless 100% merino wool sauna hats, pressed from a single piece of 3 mm felt, one size 55–61 cm, shipped from Canada.
Related reading: Do sauna hats actually work? · Merino vs regular wool vs synthetic at 90°C · Best sauna hats in Canada, compared · Does sauna heat damage your hair?