Why a millimetre chart beats a size name
Hoop earrings are sold under names like "huggie", "small" and "statement" that carry no fixed definition anywhere — unlike a Mohs hardness value or a millesimal fineness, no standards body has ever agreed where one category ends and the next begins. Different retailers draw those lines a few millimetres apart from each other, which means the same physical hoop can be labelled "medium" on one listing and "large" on another with neither retailer being wrong, exactly the way "petite" and "regular" mean different waist measurements at different clothing brands.
What does not move is the millimetre figure itself: a hoop specified at 30 mm outside diameter is 30 mm regardless of which retailer's size name it is filed under. Drawing every size on the same scale, rather than listing them as a table of names, turns an unreliable label into a comparison you can actually see and check against a hoop already in a jewellery box.
The rough bands in common use
Huggie hoops sit closest to the ear, typically under about 12 mm, hugging the lobe directly with almost no visible gap beneath. Small hoops, roughly 12 to 25 mm, clear the lobe for a subtle everyday look without hanging noticeably. Medium hoops, about 25 to 40 mm, are the size stocked most widely across mainstream retailers — visible without dominating the face, and the band most people mean by "a normal hoop". Large hoops, roughly 40 to 60 mm, hang clearly below the lobe and move with the head. Oversized hoops, upward of about 60 mm, are a deliberate statement size, more common in runway and costume pieces than everyday retail.
These bands overlap in practice between different sellers, and the boundaries above represent one consistent, non-overlapping reading of the ranges commonly published rather than a figure any single authority has fixed. Treat the band as a rough orientation and the millimetre figure as the number worth trusting.
What the diameter figure on a listing actually measures
Almost every hoop listing states the outside diameter — the widest point across the ring, wire included — because that is the single dimension easiest to measure consistently across very different hoop styles, from a plain tube to a chunky twisted design. It is not the same as the interior opening the earlobe passes through, which is smaller by roughly twice the wire thickness and varies more between styles of similar outside diameter. For a chunkier hoop, the interior clearance can matter more than the headline number, and it is worth checking separately if the wire looks unusually thick in a photograph.