Ring Size Calculator
Enter your inner ring diameter or finger circumference to estimate your size in US, EU, and VN formats. This tool belongs to the Size & Measurement category, so you can move from measurement to fit planning without leaving the same workflow.
If you are measuring for a gift, compare the result with our Bracelet Size Calculator. If you are ready to create the final piece, open the bracelet designer or explore birthstone bracelet ideas for inspiration.
Ring Size Calculator
Enter your inner ring diameter or finger circumference in millimeters to estimate your US, EU, and VN size reference instantly.
Reference-style sizing chart
This view now behaves more like a ring size chart: a clean grid, one clear shape, and the size value placed directly inside the diagram.
Ring Sizer in MM
Your size is
7
Ring Diameter
17.30 mm
Converted
US 7 / O / Ni 17.3
Drag to adjust
17.3 mm
Tip: use a flexible measuring tape for circumference, or measure the inside diameter of an existing ring with a ruler and enter the result in millimeters.
Mode
Inside diameter
Measured
17.3 mm
Converted ring
7 / O / Ni 17.3
US Size
7
UK Size
O
EU Size
54
JP Size
14
VN Size
Ni 17.3
Estimated Diameter
17.3 mm
Estimated Circumference
54.3 mm
How to read this result
EU size is based on inner circumference in millimeters. VN size is shown as a local diameter-based reference using the nearest inner diameter measurement.
This result is rounded to the nearest common ring size chart entry.
Reference Chart
Common US, UK, EU, JP, and VN ring size chart
US American | UK British | Diameter (mm) Inner | EU European | JP Japanese | VN Vietnamese |
|---|---|---|---|---|---|
| 3 | F 1/2 | 14.1 | 44 | — | Ni 14.1 |
| 3.5 | G | 14.5 | 46 | 5 | Ni 14.5 |
| 4 | H 1/2 | 14.9 | 47 | 7 | Ni 14.9 |
| 4.5 | J | 15.3 | 48 | 8 | Ni 15.3 |
| 5 | K | 15.7 | 49 | 9 | Ni 15.7 |
| 5.5 | L | 16.1 | 51 | 11 | Ni 16.1 |
| 6 | M | 16.5 | 52 | 12 | Ni 16.5 |
| 6.5 | N | 16.9 | 53 | 13 | Ni 16.9 |
| 7 | O | 17.3 | 54 | 14 | Ni 17.3 |
| 7.5 | P | 17.7 | 56 | 15 | Ni 17.7 |
| 8 | Q | 18.2 | 57 | 17 | Ni 18.2 |
| 8.5 | R | 18.6 | 58 | 18 | Ni 18.6 |
| 9 | S | 19.0 | 60 | 19 | Ni 19.0 |
| 9.5 | T | 19.4 | 61 | 20 | Ni 19.4 |
| 10 | U | 19.8 | 62 | 21 | Ni 19.8 |
| 10.5 | V | 20.2 | 63 | 23 | Ni 20.2 |
| 11 | W | 20.6 | 65 | 24 | Ni 20.6 |
| 11.5 | X | 21.0 | 66 | 25 | Ni 21.0 |
| 12 | Y | 21.4 | 67 | 27 | Ni 21.4 |
| 12.5 | Z | 21.8 | 68 | 28 | Ni 21.8 |
| 13 | Z+1 | 22.2 | 70 | 29 | Ni 22.2 |
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How this tool calculates your ring size
The calculator accepts one of two measurements: inner diameter or finger circumference. If you enter circumference, the tool converts it to diameter by dividing circumference by pi. It then compares that diameter with a standard ring size chart and returns the nearest common US size.
EU size is usually expressed as the inner circumference in millimeters, so the tool returns the closest matching circumference-based number. VN size is shown as a local diameter-based reference, which is useful when a jeweler asks for the inside diameter directly.
For best accuracy, measure your finger at the end of the day, avoid measuring when your hands are unusually cold, and if you are between sizes, choose the larger size for wider bands.
Small fingers
Diameter 15.7 mm
US 5 · EU 49 · VN Ni 15.7
Average fit
Circumference 54.4 mm
US 7 · EU 54 · VN Ni 17.3
Larger fit
Diameter 18.9 mm
US 9 · EU 60 · VN Ni 18.9
FAQ
Ring sizing questions
Should I use diameter or circumference for ring sizing?
Use whichever measurement you can collect more accurately. Diameter works well when you already have a ring to measure. Circumference is better when measuring the finger directly with a soft tape or paper strip.
Why does my ring size change during the day?
Finger size can shift with temperature, hydration, and time of day. Measuring at the end of the day usually gives a more realistic everyday fit than measuring early in the morning.
Should I size up for wider rings?
Often yes. Wider bands cover more skin and can feel tighter than thin bands, so moving up slightly can improve comfort if you fall between standard sizes.
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