Hat sizing is the most consistently confusing element of hat buying. Three different sizing systems are in common use simultaneously -- metric, US fractional, and generic S/M/L -- none of which are directly interchangeable, and some brands use their own internal sizing that corresponds to none of the three. The result is that most people buy hats in the wrong size and either accept an uncomfortable fit or give up on hat wearing. The measurement process takes 60 seconds and solves the problem permanently.
The Three Hat Sizing Systems
Metric (Centimeters)
The most straightforward system. A hat labeled 58 fits a 58 cm head circumference. Used by most European hat manufacturers and increasingly in international retail. The cleanest system because the number on the label corresponds directly to a physical measurement the buyer can verify.
US Sizing (Fractional)
US hat sizes are derived from dividing the head circumference in inches by pi (approximately 3.14159), which converts the circular circumference to the hat block diameter. A head with a 58 cm circumference has a diameter of approximately 7.28 inches when calculated this way, which rounds to the US hat size of 7 1/4.
US hat sizes typically run from size 6 5/8 (approximately 53 cm) to size 8 (approximately 64 cm). The increments are 1/8 of a hat block inch, which converts to approximately 1 cm in head circumference. Understanding US sizing is primarily useful for purchasing from American hat retailers and for identifying vintage American hats by size markings.
Generic Sizing (S/M/L/XL)
The least reliable system because there is no industry standard. A size M from one manufacturer may correspond to a different head circumference than a size M from another. When purchasing using generic sizing, always verify against the brand's sizing chart that lists the actual centimeter range for each size. Never assume that S/M/L sizes are consistent across brands.
How to Take an Accurate Head Measurement
The head measurement for hat sizing is the circumference of the head at the widest point of the head above the ears. This corresponds to where the hat sweatband will sit when the hat is worn at its correct position.
What you need: A flexible measuring tape (cloth or plastic) or a strip of paper, ribbon, or string that can be measured against a ruler after.
Step-by-step:
- Stand in front of a mirror. If measuring with the help of another person, stand with your head level.
- Place the measuring tape approximately 1 cm above the tops of the ears and across the mid-forehead, above the eyebrows. This is the wearing position where the sweatband will sit.
- Pull the tape snug -- firm contact with the head, not pulled tight enough to compress the skin significantly. The tape should lie flat against the head without gaps.
- Read the circumference in centimeters at the point where the tape end meets the zero mark. Record this number.
- Measure again to confirm -- it is easy to vary the tape position by 0.5-1 cm between attempts. Two measurements that are within 0.5 cm of each other are reliable; two that differ by more than 1 cm suggest the technique needs adjustment.
For paper/string method: Wrap the paper or string around the head at the measurement line described above. Mark the point where the end meets the rest of the strip. Lay flat against a ruler and measure the distance to the mark in centimeters.
What to Do With the Measurement
A head circumference of 58 cm should fit any hat labeled 58 (metric), size 7 1/4 (US), or a size L from a brand whose chart shows L corresponds to 58 cm.
For head circumferences that fall between standard sizes -- for example, 58.5 cm, between a 58 and a 59 -- choose based on material:
- Felt hats with leather sweatbands: Choose the smaller size (58). Leather sweatbands soften and expand with wear; the fit will improve over 2-4 weeks of regular wearing.
- Straw hats: Choose the larger size (59). Straw does not break in the way felt does; a slightly snug straw hat will remain snug or become uncomfortable with heat expansion on a warm day.
- Cotton or fabric hats: Either size works, depending on whether you prefer a snug or relaxed fit. Fabric hats are less sensitive to 1 cm fit variations than structured felt or straw hats.
Head Shape and Interior Fit
Head circumference determines the size, but head shape determines the interior fit. Two people with identical 58 cm circumferences may have heads that are very round (nearly equal front-to-back and side-to-side measurements) or noticeably oval (longer front-to-back than side-to-side). The interior block shape of the hat interacts with the head shape:
Round interior block: Suits round heads. An oval head will feel pressure at the sides and have gaps at the front and back.
Oval interior block: Suits oval heads. A round head will feel pressure at the front and back and have gaps at the sides.
Most hat manufacturers block to a slightly oval shape because the majority of heads are oval. Some manufacturers specifically offer round-blocked and oval-blocked versions of the same hat. When ordering online from a quality hat brand, check if they offer multiple interior shapes -- if so, measure your head in both dimensions (front-to-back and side-to-side) to determine your head shape category.
Adjusting Fit After Purchase
Hat Too Large by Small Margin (0.5-1 cm)
Hat sizing tape -- foam or felt tape adhered to the interior of the sweatband -- reduces the effective circumference. Available at hat retailers, craft stores, and online. Apply in short strips to the area where the hat is loosest (often the sides or back for slightly-too-large hats). Check the fit after each strip addition.
Hat Too Small by Small Margin (0.5-1 cm)
A hat stretcher expands felt hats gradually. The wooden or metal stretcher is inserted into the hat and expanded, with light moisture (steam from a kettle or clothes steamer applied to the interior) helping the felt relax. Expand slowly -- overnight stretching with light steam is safer than forced same-day stretching. This method works for wool and rabbit fiber felt; straw hats cannot be meaningfully stretched without damage.
Hat Too Large or Small by More Than 1 cm
Exchange for the correct size. Adjustment methods beyond 1 cm of circumference risk damaging the hat structure or producing an uneven, uncomfortable fit. The correct size is the correct solution.
Find quality hats in a full range of metric sizes in the Hatloom collection.
Frequently Asked Questions
What is the average head size for men?
The most common head circumference for men is 57-58 cm, corresponding to US hat size 7 1/8 to 7 1/4. However, significant variation exists -- a meaningful proportion of men have heads below 56 cm or above 60 cm, and hat shopping consistently produces more frustration for these wearers because retail stock concentrates in the most common sizes. Measuring specifically is always more reliable than assuming average.
What is the average head size for women?
The most common head circumference for women is 56-57 cm, corresponding to US size 7 to 7 1/8. Women's hat retail typically stocks a narrower size range than men's, which can make finding the correct size more challenging for women at the extremes of the distribution. Many hat buyers assume women's hat fit issues are about style rather than size -- but a disproportionate number of cases where a woman concludes a hat doesn't suit her are actually size issues in disguise.
How do I convert my hat size to a different sizing system?
The metric measurement is the universal reference. To convert: measure in centimeters (or convert the circumference measurement you have to centimeters). From centimeters, US sizing is calculated as: circumference in inches divided by pi; round to the nearest 1/8. From centimeters, UK sizing is identical to US in most contexts. For generic S/M/L, check the specific brand's sizing chart and match your centimeter measurement to the listed range for each size.
My head is exactly between two standard sizes. Which size hat should I buy?
See the guidance above by material. The general rule for between-sizes is: try both if possible. In felt hats, the smaller size is usually the better choice because the sweatband break-in will improve the fit. In straw and rigid hats, the larger size is safer because there is no break-in mechanism. If trying on is not possible, the smaller size in felt, the larger size in straw, is the decision rule.
Why does the same hat size feel different across different brands?
Interior block shape (round vs. oval) and actual construction tolerances. Even when both hats are labeled 58 cm, the block used to shape them may have different interior dimensions from front-to-back vs. side-to-side, fitting different head shapes differently. Additionally, some manufacturers measure their blocks differently or have production tolerances that create variation between nominal and actual interior dimensions. A hat that fits correctly from one brand in size 58 may require size 59 from a brand that runs small, or size 57 from one that runs large. When purchasing from a new brand, verify sizing against the brand's specific chart and allow for one exchange if the size is wrong.
