Digital Calibration & Sizing Engine
Standard:ISO 8653:2016
STEP 1
Calibrate Screen Scale
Hold your debit or credit card vertically flat against the box below. Adjust until the outline matches the short edge (53.98 mm) of your card.
Short Edge (53.98 mm)Physical Card Target204 px
STEP 2Match Your Ring17.30 mm
Place your ring on the circle below. Adjust slider until circle fills the inside diameter.
US 717.3 mm
US 3 (14.1 mm)US 13.5 (22.6 mm)
Direct Dimensions Input
mm
mm
Equivalent units:
5.44 cm|2.14 in
International Sizing Scale
US / Canada7
UK / AustraliaN 1/2
Europe (ISO)54
India / Asia14
Measurement Protocol
ISO 8653:2016 CompliantThree methods for precision fit.
01 / APERTURE
Direct Ring Matching
Place an existing ring on your screen. Use any debit card to calibrate display density for true physical millimeter accuracy.
02 / CIRCUMFERENCE
Paper Wrap Method
Wrap a non-stretchy strip of paper snugly around your finger base. Mark the overlap, measure with a flat ruler in millimeters, and enter the circumference.
03 / COMPENSATION
Knuckles & Band Width
If your knuckle is larger than the base, choose the midpoint. For statement bands wider than 6mm, increase by a half size.
Universal Standards
International Ring Size Matrix
ISO 8653
| US / Canada | UK / Australia | Europe (ISO) | India / Asia | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.1 | 44.2 |
| 3.5 | G | 45 | 5 | 14.5 | 45.5 |
| 4 | H | 47 | 7 | 14.9 | 46.8 |
| 4.5 | I | 48 | 8 | 15.3 | 48.0 |
| 5 | J 1/2 | 49 | 9 | 15.7 | 49.3 |
| 5.5 | K 1/2 | 51 | 10 | 16.1 | 50.6 |
| 6 | L 1/2 | 52 | 11 | 16.5 | 51.9 |
| 6.5 | M 1/2 | 53 | 13 | 16.9 | 53.1 |
| 7 | N 1/2 | 54 | 14 | 17.3 | 54.4 |
| 7.5 | O 1/2 | 56 | 15 | 17.7 | 55.7 |
| 8 | P 1/2 | 57 | 16 | 18.1 | 57.0 |
| 8.5 | Q 1/2 | 58 | 17 | 18.5 | 58.3 |
| 9 | R 1/2 | 59 | 18 | 18.9 | 59.5 |
| 9.5 | S 1/2 | 60 | 19 | 19.3 | 60.8 |
| 10 | T 1/2 | 62 | 20 | 19.8 | 62.1 |
| 10.5 | U 1/2 | 63 | 22 | 20.2 | 63.4 |
| 11 | V 1/2 | 65 | 23 | 20.6 | 64.6 |
| 11.5 | W 1/2 | 66 | 25 | 21.0 | 65.9 |
| 12 | Y | 67 | 26 | 21.4 | 67.2 |
| 12.5 | Z | 68 | 27 | 21.8 | 68.5 |
| 13 | Z+1 | 70 | 28 | 22.2 | 69.7 |
| 13.5 | Z+2 | 71 | 29 | 22.6 | 71.0 |
Printable Tool
Get Printable PDFNeed a physical cutout sizer?
Download our free 100% scale paper strip and circular cutouts sheet with integrated bank card calibration bar.
Documentation & FAQ
Frequently Asked Questions.
What is 7 cm in ring size?
A 7 cm (70 mm) finger circumference equals a US Size 13, UK Size Z+1, European Size 70, and Asian Size 28 to 29.
Is a size 7 ring big for a woman?
No. A US size 7 (17.3 mm inner diameter, 54.4 mm circumference) is the worldwide average ring size for women.
Can I measure my ring size on my phone?
Yes. Use our on-screen tool, place a standard bank card on screen to calibrate the pixel ratio 1:1, and position your ring over the circle.
How many mm is a US size 6 ring?
A US size 6 ring has an inside diameter of 16.5 mm and an inner circumference of 51.9 mm (UK size L 1/2, EU size 52).
What should I do if I am between two ring sizes?
Always size up. Fingers naturally swell in the evening and during warmer temperatures, and wide bands (6mm+) fit tighter than thin bands.