Ring Size Converter
Enter your US ring size to find the equivalent European size (inner circumference in mm) and an approximate UK letter size. Essential when ordering rings from international jewelers or shopping online from brands that use different sizing systems.
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Formula
EU Size (mm) = (US Ring Size × 2) + 40.4
US ring sizes are based on finger circumference in increments of approximately 0.8 mm. The EU system directly measures inner circumference in millimeters. The formula US × 2 + 40.4 approximates the standard conversion; the UK system uses letter codes that roughly correspond to this calculator's numerical UK approximation (letters A through Z).
How to use the Ring Size Converter
- 1
Enter your us ring size
- 2
Read your results instantly
Results update in real time as you type.
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How Ring Sizes Are Measured
US ring sizes are dimensionless numbers running roughly from 3 to 13 for adults. Each half-size represents approximately 0.4 mm of inner diameter (about 1.27 mm of circumference). European sizes are the inner circumference in millimeters — a much more intuitive system. UK sizes use letters (A through Z+) and are based on the same circumference measurements as the EU system, just encoded differently. Jewelers can measure your exact size with a ring mandrel or sizing rings.
Getting an Accurate Ring Size
Fingers change size with temperature, time of day, and hydration. Measure when your fingers are at normal temperature (not cold or swollen from heat). Measure multiple times at different points in the day and average the results. String method: wrap a strip of paper or string around your finger, mark the overlap, measure the length in mm — that is your EU size. Most US ring sizes 4-10 fit the majority of adult fingers; women average US size 6-7, men US size 9-10.
Tips & Insights
Measure Multiple Times
Finger size fluctuates by 0.5 to 1 full US size depending on temperature and time of day. Average three measurements at different times for the most reliable size.
When in Doubt, Size Up
A ring that is slightly too large can be resized down more easily than one that is too small. For comfort fit or thick bands, go a half size up from your measured size.
Different Fingers, Different Sizes
Your ring finger size on your dominant hand is often 0.5 size larger than the non-dominant hand. Measure the specific finger you plan to wear the ring on.
Worked Examples
US Size 7 (average women's)
EU 54.4 mm, UK approx 15, 54.4 mm circumference.
US Size 10 (average men's)
EU 60.4 mm, UK approx 21, 60.4 mm circumference.
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Frequently Asked Questions
What is the average ring size for women?
The average US women's ring size is 6-7. The average men's ring size is 9-10.
How accurate is this conversion?
The formula gives a close approximation. For high-value jewelry, always verify with the jeweler's specific size chart or have your finger measured professionally.
Can a ring be resized?
Most metal rings can be resized by 1-2 sizes up or down by a jeweler. Rings with stones all around the band or very thick bands may be more difficult or impossible to resize.
What is the EU ring size system?
European ring sizes represent the inner circumference of the ring in millimeters. A EU 54 ring has an inner circumference of 54 mm.
How do I measure my ring size at home?
Wrap a thin strip of paper around your finger, mark where it overlaps, measure the length in mm — that is your EU size. Divide by PI to get inner diameter in mm.
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