How accurate are online ring size converters?

Most reputable ring size converters, including this one, are based on ISO 8653 and common jeweler charts. They are accurate enough for everyday use, but tolerances of ±0.1–0.2 mm in diameter and differences between brands mean you should still confirm with a jeweler if the ring is expensive or non‑returnable.

Should I use inner diameter or circumference to find my ring size?

If you have an existing ring that fits well, measuring the inner diameter with a caliper is usually the most reliable. If you only have a strip of paper or string, measure the inner circumference around your finger. The converter accepts both and will show the closest standard size.

Do ring sizes change with temperature or time of day?

Yes. Fingers are usually slightly larger in the evening, in hot weather, during pregnancy, or after salty food and alcohol. They are slimmer in the morning and in cold conditions. For best results, measure at the end of the day when your hands are warm and not swollen.

What if I am between two ring sizes?

If you are between sizes, most jewelers recommend choosing the larger size, especially for wider bands, hot climates, or if your knuckles are prominent. For thin bands or if your fingers shrink in cold weather, the smaller size may feel more secure. When in doubt, try both at a jeweler.

Ring Size Converter – US, UK, EU, Italy, Japan & Inner Diameter

How this ring size converter works

This tool uses a reference table of standard ring sizes from US, UK, EU, Italy, Japan and China. Each size is associated with an inner diameter in millimeters. From the diameter we compute the inner circumference and convert between systems.

Formulas used

Inner circumference from diameter:

\( C = \pi \times D \)

C = inner circumference (mm)
D = inner diameter (mm)
\( \pi \approx 3.14159 \)

Conversion between mm and inches:

\( \text{inches} = \dfrac{\text{mm}}{25.4} \)

Supported ring size systems

US / Canada – numeric sizes including half sizes (e.g. 5, 5.5, 6).
UK / Australia / Ireland – letter sizes with half steps (e.g. L, L½, M).
EU – usually inner circumference in mm (e.g. 52, 54).
Italy – numeric system offset from EU by a few sizes.
Japan – numeric sizes commonly used in Asia.
China – approximate mapping based on popular charts.

How to measure your ring size at home

1. Using an existing ring (most accurate)

Choose a ring that fits the intended finger comfortably.
Measure the inner diameter across the widest point of the inside circle using a ruler or, ideally, a caliper.
Enter the value in millimeters under Inner diameter in the converter.
The tool will highlight the closest standard size and show all equivalents.

2. Using a strip of paper or string

Cut a thin strip of paper or use non‑stretchy string.
Wrap it around the base of your finger where the ring will sit.
Mark where the ends meet, then measure the length in millimeters.
Enter this value as Inner circumference in the converter.

Tips for an accurate fit

Measure at the end of the day when your fingers are warm.
Measure several times and use the average.
Consider the ring style: wider bands often feel tighter and may need a slightly larger size.
If you are between sizes, most jewelers recommend choosing the larger size for comfort.

Frequently asked questions

How do I convert my ring size between US, UK and EU?

Select the system you know (for example US), choose your size, and click Convert. The tool instantly shows the matching UK letter, EU number, Italian and Japanese sizes, plus the physical diameter and circumference.

Are ring sizes unisex?

Yes. The size numbers themselves are unisex – a US 7 has the same inner diameter whether it is a “men’s” or “women’s” ring. Marketing labels differ, but the physical measurements are the same.

Why do different charts show slightly different values?

Manufacturers round differently and may use slightly different base standards. Tolerances of ±0.1–0.2 mm in diameter are common. That is why it is always wise to confirm with a jeweler, especially for expensive or non‑returnable rings.

Can I use this converter for wide bands or stacking rings?

Yes, but keep in mind that wide bands and multiple stacked rings feel tighter. Many people go up by about half a size for very wide bands.

Ring Size Converter

Equivalent ring sizes

Ring size conversion chart