cm → mm Ring Measurement Converter
Jewelers, makers, and DIY enthusiasts can quickly translate ring measurements into millimeters for more precise sizing.
Use a flexible tape measure or calipers for best accuracy.
Converted Measurements
5.400 cm
Input
54.00 mm
Converted value
17.19 mm
Inside diameter
Inside circumference: 54.00 mm
Approximate US Ring Sizes
Compare the converted diameter to common US ring sizes below. Always confirm with a jeweler for the final fit—finger size can vary with temperature and time of day.
| US Size | Diameter (mm) | Circumference (mm) |
|---|---|---|
| 5 | 15.7 | 49.3 |
| 6 | 16.5 | 51.9 |
| 7 | 17.3 | 54.4 |
| 8 | 18.2 | 57.2 |
| 9 | 19.0 | 59.8 |
| 10 | 19.8 | 62.3 |
| 11 | 20.6 | 64.8 |
| 12 | 21.4 | 67.3 |
How to Use This Converter
Measure your ring or finger
Use a soft measuring tape for circumference or calipers for diameter.
Select the measurement type
Tell the calculator whether you measured circumference or diameter.
Enter centimeters
We instantly convert to millimeters and show both circumference and diameter.
Formula
Circumference (mm) = Circumference (cm) × 10
Diameter (mm) = Circumference (mm) ÷ π
Example: 5.4 cm circumference → 54.00 mm.
Helpful Tips
- Measure at room temperature—fingers can swell or shrink with temperature.
- Measure at the end of the day when fingers are largest for a comfortable fit.
- For wide bands, size up slightly to accommodate added thickness.
- Use the Ring Size converter to map mm measurements to local size charts.
Frequently Asked Questions
Can I convert directly to US/UK ring sizes?
Use the displayed diameter to compare against the included reference table or our ring-size calculators.
What if my measurement falls between sizes?
Most jewelers recommend rounding to the nearest 0.25 size or trying sample rings for confirmation.
Does this work for printable ring guides?
Yes—enter the circumference in cm from a printable guide to convert to millimeters and ring sizes.
How accurate is the conversion?
Conversion from cm to mm is exact (×10). The diameter/circumference relationship uses π (~3.14159).