This chart is a guide to help you work out your ring size. Marianne makes rings following British sizing guides. Please use this chart to gauge the closest equivalent size to your country sizing scale. Please see information about ordering your correct ring size in the FAQ section.
| British Size | Inside Diameter mm | USA Size | Inside Diameter mm | European Size | Inside Diameter mm | Japan Size | Inside Diameter mm |
| A | 11.97 | 0.5 | 11.97 | ||||
| B | 12.36 | 1 | 12.37 | 1 | 13.04 | 1 | 13.00 |
| C | 12.75 | 1.5 | 12.78 | 2 | 13.36 | 2 | 13.33 |
| D | 13.14 | 2 | 13.21 | 3 | 13.67 | 3 | 13.66 |
| E | 13.53 | 2.5 | 13.61 | 4 | 13.99 | 4 | 14.00 |
| F | 13.92 | 3 | 14.05 | 5 | 14.31 | 5 | 14.33 |
| G | 14.31 | 3.5 | 14.45 | 6 | 14.63 | 6 | 14.66 |
| H | 14.70 | 4 | 14.86 | 7 | 14.95 | 7 | 15.00 |
| I | 15.09 | 4.5 | 15.27 | 8 | 15.27 | 8 | 15.33 |
| J | 15.48 | 5 | 15.70 | 9 | 15.58 | 9 | 15.66 |
| K | 15.87 | 5.5 | 16.10 | 10 | 15.90 | 10 | 16.00 |
| L | 16.26 | 6 | 16.51 | 11 | 16.22 | 11 | 16.33 |
| M | 16.65 | 6.5 | 16.92 | 12 | 16.54 | 12 | 16.66 |
| N | 17.04 | 7 | 17.35 | 13 | 16.86 | 13 | 17.00 |
| O | 17.45 | 7.5 | 17.75 | 14 | 17.17 | 14 | 17.33 |
| P | 17.86 | 8 | 18.19 | 15 | 17.49 | 15 | 17.66 |
| Q | 18.27 | 8.5 | 18.59 | 16 | 17.81 | 16 | 18.00 |
| R | 18.68 | 9 | 18.89 | 17 | 18.13 | 17 | 18.33 |
| S | 19.09 | 9.5 | 19.41 | 18 | 18.45 | 18 | 18.66 |
| T | 19.50 | 10 | 19.84 | 19 | 18.76 | 19 | 19.00 |
| U | 19.91 | 10.5 | 20.20 | 20 | 19.08 | 20 | 19.33 |
| V | 20.32 | 11 | 20.24 | 21 | 19.40 | 21 | 19.66 |
| W | 20.73 | 11.5 | 20.68 | 22 | 19.72 | 22 | 20.00 |
| X | 21.14 | 12 | 21.08 | 23 | 20.04 | 23 | 20.33 |
| Y | 21.55 | 12.5 | 21.49 | 24 | 20.35 | 24 | 20.66 |
| Z | 21.96 | 13 | 21.89 | 25 | 20.67 | 25 | 21.00 |
| 13.5 | 22.33 | 26 | 20.99 | 26 | 21.33 | ||
| 27 | 21.31 | 27 | 21.66 | ||||
| 28 | 21.63 | ||||||
| 29 | 21.94 | ||||||
| 30 | 22.26 |
