When should I measure my finger?

Warm, and late in the day. Fingers are smallest when cold and in the morning, and a ring sized then will be uncomfortable later.

Conversionsapparel

Ring Size Converter

Ring sizes across US, UK and EU systems. The EU size is just the inside circumference in millimetres, which makes it the one worth measuring in.

Also called: ring size chart, us to uk ring size.

Inside circumference

54 mm circumference, 17.19 mm diameter. That is US 9.75, UK N and EU size 54. Measure warm and late in the day. Fingers are smallest in the morning and in the cold.

Inside diameter

17.19

US size

9.75

UK letter

EU size

On measuring

Measure warm and late in the day. Fingers are smallest in the morning and in the cold.

How this is calculated

Method and background

How this is calculated

Circumference and diameter relate by pi, and the EU size is the circumference in millimetres directly. US sizes step by about 0.8 mm of circumference per half size, and the UK uses letters. Measuring is the fiddly part: fingers change size through the day and with temperature, so measuring warm and late in the day gives a size that will not be too tight. A wider band needs a slightly larger size than a narrow one.

the EU system is simply the circumference in millimetres, which makes it the least arbitrary of the three

C: Circumference
d: Diameter

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a 54 mm circumference

Size or measurement: 54
That is: Inside circumference in mm

Inside circumference54

Diameter is the circumference over pi, 54/3.14159

Open this example

diameter converts by pi

Size or measurement: 17.19
That is: Inside diameter in mm

Inside circumference54

boundary: the inverse of the first case

Open this example

Method and limits

What it assumes

Inside measurements of the ring, not the finger.

What it deliberately does not model

Finger size varies by up to half a size through the day and more with temperature.
Wide bands fit tighter than narrow ones at the same nominal size.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

When should I measure my finger?: Warm, and late in the day. Fingers are smallest when cold and in the morning, and a ring sized then will be uncomfortable later.