US · UK · EU · FR · DE · JP — every formula shown
What's my ring size? Convert any measurement to every system.
Measure your finger or an existing ring — circumference or diameter, in mm, cm or inches — and get your US size with UK, EU/ISO, French, German and Japanese equivalents instantly. US 7 = 54.4 mm = UK N½. That's the whole trick, and the calculator shows the math.
I have…
mm
Measure at day's end — fingers are largest then.
mm
Only if knuckles measure a full size larger than the finger base.
US size
7
UK
N½
BS 6820
EU / ISO
54
circumference mm
Japan / China
13
East-Asia
Circumference54.4 mm · 5.44 cm · 2.14 in
Inside diameter170.90 mm · 17.09 cm
French / ItalianFR 14.3 · IT 14
GermanDE 17.5
Wide bandA 2mm band is narrow enough to keep size 7 as measured.
Between sizes take the larger — rings are easier to size down. Wide bands (≥6 mm) grip more contact area: the +0.25 is already applied above when you pick a wide band.
US formula: size = (circumference mm − 36.5) ÷ 2.55 · diameter: size = (mm − 11.63) ÷ 0.8128. Between sizes, take the larger.
All 7 ring size tools
For anyone buying a ring online — and anyone sizing a surprise gift.
Ring Size Charts
View category →Ring Size Chart
Full US 3–16 chart with UK, EU, French, German and Japanese columns — filter, highlight and print.
Men's Ring Size Chart
US 8–15 chart for men, with the wide-band and knuckle adjustments that move men's sizes most.
Ring Size Chart in cm
The full chart in centimetres — 4.4 to 7.7 cm circumference with every US and UK equivalent.
Printable Ring Size Chart
A print-ready ring sizer with a credit-card calibration box — print, cut, wrap, read.
Ring Size Conversion Tool
Convert any size between US, UK, EU, French, German, Japanese and Chinese systems — both directions.
Guides
How to Measure Ring Size
Four accurate home methods — existing ring, paper strip, calibrated printable, and the gift secret-weapon.
The Complete Ring Size Guide
Every sizing system explained, quarter sizes, width and knuckle rules, and what resizing costs.
7 cm in Ring Size
Exactly what 7 cm of circumference converts to — with the math many blogs get wrong.
Average Ring Size
What the average man and woman wear, how build shifts it, and how to guess well for gifts.
Ring Size 8
Everything about US size 8: exact millimetres, international equivalents, and who wears it.
What this site does — and what it does not
It does
- Convert one measurement into all six national size systems, computed from one formula so columns agree.
- Apply the two corrections that move real fits: wide bands (6 mm+) and large knuckles.
- Keep every calculation in your browser; nothing you type is stored or sent.
It does not
- Replace a jeweller's stick sizer — if the purchase is non-resizable, get sized in store first.
- Account for unusual finger shapes or swelling conditions — those need a professional fitting.
- Guarantee a seller's listed size — convert from millimetres whenever a listing provides them.