Hat Size Converter

How hat size conversion works

Hat sizing starts with one measurement: head circumference, taken just above the eyebrows and ears, where a hat actually sits. From there the systems diverge. The EU size is the simplest — it is the circumference in centimetres, so a 57 cm head is an EU 57. The US and UK sizes divide that circumference by pi to give a diameter-based number in inches, quoted in eighths: a 57 cm head is 22.44 inches around, and 22.44 ÷ π = 7.14, which rounds to the nearest eighth as 7⅛.

Letter bands for quick shopping: most casual hats skip numbers entirely and use S, M, L and XL. On the standard bands this converter uses, S covers 54–55 cm, M covers 56–57 cm, L covers 58–59 cm, XL covers 60–61 cm and XXL covers 62 cm and up. A 57 cm head is therefore a comfortable M — but a structured cap in M fits tighter than a soft beanie in M, so the number is always the safer guide when it is printed.

Measure properly, once: use a flexible tape, keep it level and snug without pulling tight, and measure twice — hair volume alone can shift the result by a centimetre. If you fall between two eighth sizes, size up for structured hats (caps, fedoras, helmets) and down for stretchy ones. Children and teenagers use the same centimetre scale but smaller bands, so the cm figure is what matters most for them.

Why two “same” systems: US and UK hat sizes are quoted together on most charts because they share the same eighth-inch steps, though some UK makers run a fraction smaller than their US equivalents. The difference is at most an eighth — one step — so if a UK hat feels tight at your US size, the next eighth up usually fixes it. As with rings and shoes, the brand's own chart is the final word.