CM to MM Ring Size Converter
Convert ring measurements from centimeters to millimeters and find equivalent ring sizes
Ring Measurement Converter
Straight line across the ring's inner circle
Distance around the ring's inner circle
Conversion Results
Millimeter Measurements
Inch Measurements
Closest Ring Size Match
Conversion Formulas
CM to MM: Multiply by 10 (1 cm = 10 mm)
Diameter to Circumference: Circumference = Diameter × π
Circumference to Diameter: Diameter = Circumference ÷ π
MM to Inches: Divide by 25.4 (1 inch = 25.4 mm)
Ring Size Chart
| US Size | UK Size | EU Size | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 3 | F | 44 | 14.1 | 44.2 |
| 3.5 | G | 45 | 14.5 | 45.5 |
| 4 | H | 46 | 14.9 | 46.8 |
| 4.5 | I | 47 | 15.3 | 48.0 |
| 5 | J | 48 | 15.7 | 49.3 |
| 5.5 | K | 50 | 16.1 | 50.6 |
| 6 | L | 51 | 16.5 | 51.9 |
| 6.5 | M | 52 | 16.9 | 53.1 |
| 7 | N | 54 | 17.3 | 54.4 |
| 7.5 | O | 55 | 17.7 | 55.7 |
Showing first 10 sizes. Full range available in calculator.
How to Measure Ring Size
Use String or Paper
Wrap around finger where ring will sit
Mark Overlap Point
Mark where the string meets
Measure with Ruler
Measure string length in cm
Use This Calculator
Enter circumference to find size
Ring Sizing Tips
Measure at end of day when fingers are largest
Measure multiple times for accuracy
Account for knuckle size if larger
Consider ring width - wider rings fit tighter
Professional sizing is most accurate
Understanding Ring Size Conversion
Diameter vs. Circumference
Ring diameter is the straight-line distance across the ring's inner circle, while circumference is the distance around the inner circle. Both measurements are essential for accurate ring sizing.
Conversion Basics
- •1 centimeter = 10 millimeters
- •Circumference = Diameter × π (3.14159)
- •1 inch = 25.4 millimeters
International Ring Sizes
US & Canada
Numerical system (3-13)
UK & Australia
Letter system (A-Z)
Europe
Circumference in mm (44-69)