Hat size comes from one measurement: the circumference of your head where the hat's band will sit. Fitted hats convert that number into the familiar fractional sizes - 7, 7 1/4, 7 1/2 - while many casual hats use letter sizes and European labels simply print the circumference in centimetres. Measure once, carefully, and you can shop in any of the three systems using the chart below.
Use a soft dressmaker's tape. If you do not have one, wrap a non-stretch string or ribbon around your head, mark it, and measure it against a ruler - the same approach used for ring sizing, scaled up. Measure two or three times and use the largest reading; hair volume and tape angle shift the number by more than most people expect.
Where the Tape Goes
Place the tape around your head at the level where a hat band sits: across the forehead about an eighth to a quarter inch above the eyebrows, just above the ears, and around the widest part of the back of the head. Keep the tape level and snug - resting firmly on the hair without compressing it flat or digging in. A helper makes this easier, but a mirror works: check that the back of the tape has not slipped up or down before reading the number.
Measure with your hair in its usual style. Thick or long hair worn down adds measurably to the circumference, and a hat bought on a short-hair measurement can feel tight after a style change. If you wear your hair both ways, size for the larger arrangement - a slightly loose hat can be padded with a sizing strip, while a tight one has little remedy.
Fitted Hat Size Chart
US fitted sizes are the head circumference in inches divided by pi, which is why they land on eighths. The chart below gives the standard conversions; the centimetre column is also the European size.
| Head (in) | Head (cm) = EU size | US fitted size | Letter size (approx.) |
|---|---|---|---|
| 21 5/8 | 55 | 6 7/8 | S/M |
| 22 | 56 | 7 | M |
| 22 3/8 | 57 | 7 1/8 | M |
| 22 3/4 | 58 | 7 1/4 | L |
| 23 1/8 | 59 | 7 3/8 | L |
| 23 1/2 | 60 | 7 1/2 | XL |
| 23 7/8 | 61 | 7 5/8 | XL |
| 24 1/4 | 62 | 7 3/4 | XXL |
UK fitted sizes traditionally run one-eighth of a size smaller than the US size for the same head - a US 7 1/4 is a UK 7 1/8 on many British makers' charts. When a UK brand is involved, shop by the centimetre measurement rather than the fraction to avoid the offset.
Fitted, Adjustable and Letter Sizes
Fitted hats - structured caps, fedoras, bowlers - are sold in the fractional sizes above and have no adjustment, so the measurement has to be right. Adjustable hats - snapback, strapback and hook-and-loop caps - cover a range of several centimetres and forgive an approximate measurement; your chart position tells you whether you will wear the closure near its start, middle or end. Letter sizes (S/M/L/XL) are used for knit caps, sun hats and stretch styles; each letter spans about two centimetres, and brands set their own boundaries, so the letter is the least precise system of the three.
Between two fitted sizes, choose the larger. A hat one-eighth too large sits comfortably with a thin foam sizing strip inside the band; a hat one-eighth too small presses at the temples and tends to give headaches on a long wear. Head shape matters too: most hats are made on a regular oval, and long-oval heads can feel pressure front and back even at the correct circumference - some makers offer long-oval blocks for exactly this reason. Once sized, browse styles in the men's hats guide or the women's hats guide.
Common Questions
- How do I measure my head without a soft tape?
- Wrap a non-stretch string, ribbon or even a phone charging cable around your head at band level, mark where it meets, and measure the length against a ruler or metal tape. Take the largest of two or three readings.
- Do hats stretch to fit over time?
- Some materials relax slightly - knit caps stretch noticeably, and leather bands can ease with wear - but structured fitted hats and felt hats change very little. Do not count on stretch to fix a hat that is a full size too small; size up instead.
- Is a UK hat size the same as a US hat size?
- Not exactly. UK fitted sizes traditionally run one-eighth smaller than US sizes for the same head circumference, so a US 7 1/4 corresponds to a UK 7 1/8. The centimetre measurement is identical in both systems, which makes it the safest number to shop by.
- Where should a hat sit on my head?
- The band should rest level, just above the eyebrows and ears, without tilting. A correctly sized hat stays in place when you nod, does not leave a deep red mark after a short wear, and does not spin freely when you turn your head.
Measure & Convert: The Full Series
This page is part of the Apparel Search measuring and size conversion series. Browse the full series below, or start from the size guides hub.