Inches to Ring Size

Jewelry Metrology & ISO 8653:2016 Sizing Standards

Under the ISO 8653 international standard, ring sizes correspond directly to the internal circumference of the ring band in millimeters.

Primary International Ring Sizing Chart

• 2.00 Inches (50.6 mm): = US Size 5.5 = UK K 1/2 = EU 50.5 = Japan 10

• 2.08 Inches (53.1 mm): = US Size 6.5 = UK M 1/2 = EU 53.0 = Japan 13

• 2.14 Inches (54.4 mm): = US Size 7.0 = UK N 1/2 = EU 54.0 = Japan 14

• 2.22 Inches (57.0 mm): = US Size 8.0 = UK P 1/2 = EU 57.0 = Japan 16

• 2.34 Inches (59.5 mm): = US Size 9.0 = UK R 1/2 = EU 59.5 = Japan 18

• 2.44 Inches (62.1 mm): = US Size 10.0 = UK T 1/2 = EU 62.0 = Japan 20

How to Use This Calculator

Enter your Measurement in Inches (in) (e.g. 2.14 in in), Measurement Type — choose from Finger Circumference (tape/string around knuckle), Inside Ring Diameter (across inside opening), and Ring Band Width — choose from Standard Thin Band (< 4mm wide), Wide / Comfort Fit Band (6mm+ / adds +0.5 size). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Conversion factors (to SI base unit or reference unit):

us: 3.0

eu: 44.0

diam: 14.1

circ: 44.2

Worked Example

A finger circumference measurement of 2.14 inches (54.4 mm) corresponds to a standard US Size 7 for engagement and wedding bands.

Understanding Your Result

Unit conversion precision: round to the same number of significant figures as your original measurement. Converting 6 feet to meters gives 1.8288 m — but if your measurement was approximate (±1 inch), expressing more than 2 decimal places is false precision. For international trade and technical specifications, SI units (meters, kilograms, liters) are the standard. US customary units (feet, pounds, gallons) differ from Imperial UK units: 1 US gallon = 3.785 L vs. 1 UK gallon = 4.546 L.