💍 Sizing

Hat & Ring Size Converter

Find your ring or hat size in another system. Choose ring or hat, pick the system you know, enter the size, then press Convert.

Written and reviewed by SM Arijul Islam · Last reviewed 27 October 2026 · Editorial standards · Report an error

About the Hat & Ring Size Converter

Ring sizing is not one scale with different labels. US sizes step in half sizes, UK and Australian sizes use letters, EU sizes are the inner circumference in millimetres, and Japanese sizes use their own numbers. A US 7 is about a UK N, an EU 54 and a JP 14.

Hat sizing is simpler but still inconsistent. US and UK hat sizes are based on head circumference in inches divided by π, EU sizes are the circumference in centimetres, and many brands use S–XXL. Measure around the widest part of the head, about 1 cm above the ears, and keep the tape snug but not tight.

How the calculation works

US ring size ≈ 3 + (inner circumference mm − 44.2) ÷ 2.55.
EU ring size = inner circumference in millimetres.
JP ring size ≈ inner circumference mm − 40.
US hat size = head circumference in inches ÷ π.
EU hat size = head circumference in centimetres.

Reference values

Common ring-size equivalents
US ring	UK / AU	EU (mm)	JP
5	J½	49	9
6	L½	52	12
7	N½	54	14
8	P½	57	17
9	R½	59	19
10	T½	62	22
11	V½	65	25

Worked example: a 57 cm head and a 54 mm ring

A head circumference of 57 cm is a US hat size 7⅛ (57 ÷ 2.54 ÷ π = 7.14, rounded to the nearest eighth), an EU 57, and a large in many S–XXL ranges. For a ring, a 54 mm inner circumference is EU 54, about US 7 and UK N.

Measure in the evening, when fingers are slightly larger, and measure the widest part of the head about 1 cm above the ears. A ring that is too tight is uncomfortable and hard to remove; when you are between sizes, choose the larger one. For hats, choose the measured size—too large slips, too small leaves marks.

Frequently asked questions

Should I measure my finger or an existing ring?

Both, then compare. An existing ring gives the inner diameter directly; measuring your finger accounts for knuckles but is easy to make too loose.

Why do ring sizes differ between brands?

The nominal scale is standard, but comfort-fit bands, wide bands and different gauges change how a size feels. A 6 mm band usually needs a half size larger than a 2 mm band.

How do I measure hat size?

Run a soft tape around the head about 1 cm above the ears and across the mid-forehead. Keep it level and snug. If you are between sizes, choose the larger one.

Should I size up or down?

For rings, choose the larger size if you are between sizes. For hats, choose the size that matches your measurement; a hat should sit snugly without leaving marks.