21 mm ring size

The 21 mm ring size, measured straight across the inside, is about a US 11½. In the UK it is W½, and in Europe 66, and the ring is 66.0 mm round the inside.

21 mm ring size in every system

21 mm ring size: every system
US and Canada	about 11½
UK, Ireland, Australia	W½
Europe (EU)	66
Japan and China	24
India	26
Italy, Spain, Switzerland	26
Across the inside	21.0 mm · 2.10 cm · 0.827 in
Around the inside	66.0 mm · 6.6 cm · 2.60 in

Every half millimetre is a little over half a US size, so a 20.5 mm or 21.5 mm ring is the next size down or up. All of these numbers are from the standard ring size conversion table.

See a 21 mm ring at its real size

1Match a bank card

The card works like a ruler: nothing on it is read or saved, and a driving licence works too. Only its height counts, so the drawing may run off the edge of a phone. Hold the card flat on the screen, long side across, with its top edge on the drawing's top line. Then move the slider until the drawing's bottom line meets the card's bottom edge.

Optional. Only needed to lay a ring or strip on the screen; typed measurements work without it. Nothing on the card is read or saved.

2Measure

A ring I own My finger Print a sizer

Inside diameter of your ring mm

Lay the ring on the circle, or type the inside diameter if you measured it.

Length of your paper strip mm

Wrap a thin strip of paper around the base of your finger, mark where it overlaps, then measure to the mark.

The circle shows a 17.3 mm ring, drawn for a typical screen.

This size, drawn on your screen

US11½

UK W½ · EU 66 · Japan 24 · India 26

21.0 mm (0.83 in) across the inside · 65.9 mm (2.59 in) around

For a wide band (over 4 mm), go up about half a size, to US 12.

See every size in the ring size chart · Convert a size you already know

Nearby sizes

Too tight or too loose? Try the size one row up or one row down.

Nearby sizes
US and Canada	UK and Australia	Europe (EU)	Inside diameter (mm)	Circumference (mm)
10½	U½	63	20.2	63.4
10¾	V	64	20.4	64.0
11	V½	65	20.6	64.6
11¼	W	65	20.8	65.3
11½	W½	66	21.0	65.9
11¾	X	67	21.2	66.6
12	X½	67	21.4	67.2
12¼	Y	68	21.6	67.8
12½	Y½	68	21.8	68.5

Your questions on a 21 mm ring

How long is the inside of a 21 mm ring, measured all the way round?

Round the inside it is 66.0 mm, which is 6.6 cm. Straight across, it is 0.83 inches.

Which US ring size matches 21 mm across?

It is close to a US 11½. In the UK that ring is W½, and in Europe 66.