Find Your
Perfect Ring Fit
Measure at home with simple methods and accurate references - so your ring sits beautifully from the very first wear.
What Ring Size Really Means
A ring size describes the space inside the band, measured as the inner diameter or circumference in millimetres. Carat Theory follows the Canada and US scale, which runs from roughly size 3 to 13 and includes half sizes, so your fit can be set precisely rather than rounded off.
The right size pushes past your knuckle with a little resistance, then settles at the base of the finger without pinching or spinning. Because fingers swell in warmth and shrink in the cold, it is worth measuring a couple of times across the day before you decide. If you land between two sizes, the larger one is almost always the more comfortable choice.
Ways to Find Your Ring Size
Choose the method that works best for you. Each one is designed for easy at-home measuring.
Measure a Ring You Own
Choose a ring that fits the same finger well. Measure the inside diameter in millimetres, then use the conversion guide below.
Measure with a Paper Strip
Wrap a paper strip or soft tape around your finger, mark where it overlaps, lay it flat, and measure the length.
Visit a Jeweller
For special pieces, professional sizing is the most reliable option, especially for engagement rings and wider bands.
Ring Size Conversion Guide
Use this guide to convert between common ring sizing standards.
| Diameter (mm) | Circumference (mm) | Canada / US | UK / Australia | Europe |
|---|---|---|---|---|
| 14.1 | 44.2 | 3 | F | 44 |
| 14.9 | 46.8 | 4 | H | 46.5 |
| 15.7 | 49.3 | 5 | J 1/2 | 49 |
| 16.5 | 51.9 | 6 | L 1/2 | 51.5 |
| 17.3 | 54.4 | 7 | N 1/2 | 54 |
| 18.1 | 57.0 | 8 | P 1/2 | 56.5 |
| 18.9 | 59.5 | 9 | R 1/2 | 59 |
| 19.8 | 62.1 | 10 | T 1/2 | 61.5 |
| 20.6 | 64.6 | 11 | V 1/2 | 64 |
| 21.4 | 67.2 | 12 | X 1/2 | 66.5 |
| 22.3 | 70.0 | 13 | Z 1/2 | 69 |
Tip: If you are between sizes, we generally recommend choosing the larger size or a half size for comfort.
Helpful Tips
Temperature matters
Fingers can change size with heat and cold. Measure at room temperature.
Time of day
Fingers are usually slightly larger later in the day.
Band width
Wider bands feel tighter. If between sizes, size up.
Stacking rings
For stacked rings, consider going half a size up for added comfort.
Can Rings Be Resized?
Gold rings can often be resized, but certain settings and full-eternity styles may be limited. Significant resizing can affect the design, so choosing the closest size from the start is best.
Design your ring in the Ring Studio ›Shopping for someone special?
Borrow a ring they already wear on the same finger and compare its inside diameter with the conversion chart above.
View the size chart ›Ring Size FAQs
How can I measure my ring size at home?
What do ring size numbers actually mean?
How do I find out someone's ring size without asking?
What is the average ring size?
Can a lab-grown diamond ring be resized?
How do Canada, US, UK, and European ring sizes compare?
Still Unsure?
Need personalized help?
Our Carat Theory concierge team is here to help you find your perfect fit.