Quick Answer

A finger circumference of 54.4 mm corresponds to US size 7, UK size N, and EU size 54. The inner diameter for that size is approximately 17.32 mm.

Find Size from Circumference

Finger Circumference (mm)

Find Size from Diameter

Ring Inner Diameter (mm)

Common Examples

Input	Result
Circumference 49.3 mm	US 5, UK J, EU 50
Circumference 57.0 mm	US 8, UK P, EU 57
Diameter 17.32 mm	US 7, UK N, EU 54
Circumference 62.1 mm	US 10, UK T, EU 62
Diameter 19.84 mm	US 10, UK T, EU 62

How It Works

Ring sizes are based on the inner circumference of the ring, measured in millimeters. Each sizing system (US, UK, EU) maps specific circumference ranges to named sizes. The relationship between diameter and circumference is:

Circumference = Diameter x pi (3.14159)

Diameter = Circumference / pi

The standard ring size chart maps circumference values to sizes across three systems:

• US sizes run from 3 to 13 in half-size increments. Each half size adds approximately 1.2 to 1.3 mm of circumference.
• UK sizes use letters from F to Z, corresponding to the same circumference values as US sizes 3 through 13.
• EU sizes are numeric and based on the circumference rounded to the nearest whole or half millimeter.

This calculator finds the closest standard size to a given measurement. Because fingers can swell or shrink with temperature and time of day, a measurement that falls between sizes is matched to the nearest standard value.

Worked Example

For a finger circumference of 54.4 mm: The table shows 54.4 mm maps directly to US size 7, UK size N, EU size 54. The diameter is 54.4 / 3.14159 = 17.32 mm. For a measurement of 55.0 mm, the closest standard circumference is 55.7 mm (US 7.5) since

55.0 - 55.7

= 0.7 is less than

55.0 - 54.4

= 0.6. In this case the calculator would match to US 7 since 0.6 < 0.7.

For a ring with inner diameter of 19.84 mm: Circumference = 19.84 x 3.14159 = 62.33 mm. The closest standard circumference is 62.1 mm, which corresponds to US 10, UK T, EU 62.

Related Calculators

Weight Converter

Convert between pounds, kilograms, ounces, grams, and stone instantly.

Temperature Converter

Convert between Fahrenheit, Celsius, and Kelvin instantly.

Frequently Asked Questions

How do I measure my ring size at home?

Wrap a thin strip of paper or string snugly around the base of your finger, mark where it overlaps, and measure the length in millimeters. This gives the circumference. Alternatively, measure the inner diameter of a ring that already fits well using a ruler.

Why does my ring size seem different at different times of day?

Fingers change size throughout the day due to temperature, humidity, and activity level. Fingers tend to be smallest in the morning and largest in the evening. For the most accurate measurement, measure your finger at the end of the day when your hands are warm.

What is the difference between US, UK, and EU ring sizes?

US sizes are numeric (3 through 13 with half sizes). UK sizes use letters (F through Z). EU sizes are numeric and roughly correspond to the inner circumference in millimeters. All three systems describe the same physical ring dimensions using different naming conventions.

What if my measurement falls between two sizes?

The calculator finds the closest standard size. If ordering a ring, it is generally safer to choose the slightly larger size, since rings that are too tight are more uncomfortable than rings that are slightly loose.

Is ring size the same for all fingers?

No. Each finger on each hand can be a different size. The dominant hand is often slightly larger. Always measure the specific finger the ring will be worn on.