Ring Size Calculator & Chart UK US EU International Guide ISO 8653

International Ring Size Chart

Compare UK, US and EU ring sizes using inner diameter in millimetres. This table follows the ISO 8653 standard guidance. If you are unsure, get in touch for help choosing a comfortable fit for vintage and antique rings.

Measurements reflect common guidance for ISO 8653. Minor variations can occur due to rounding or regional practice. For the most accurate result, use a physical ring sizer or visit a local jeweller.

How to measure your ring size at home

The simplest way is to measure a ring that already fits. Use a rigid ruler or callipers to measure the inner diameter in millimetres. Enter that number in the calculator to see the closest UK, US and EU sizes. If you do not have a ring, wrap a narrow paper strip around your finger, mark the join and measure the length in millimetres to get the inner circumference.

Ring size FAQs

How do I measure my ring size at home?

Measure the inner diameter of a ring that fits using a ruler or callipers in millimetres. Or wrap a narrow paper strip around your finger, mark the join, measure the length for inner circumference, then divide by 3.1416 to estimate diameter.

What is the most accurate way to measure ring size?

Use a jeweller’s metal ring gauges or callipers reading to 0.1 mm at room temperature. ISO 8653 sizing is based on inner diameter.

Should I use inner diameter or inner circumference?

Inner diameter is the ISO 8653 standard and is the most consistent. Circumference is fine if converted carefully to diameter.

When is the best time of day to measure ring size?

Later in the day at room temperature. Avoid measuring in cold conditions or straight after exercise, heat or salty meals.

Should I size up for a wide band?

Often yes. Wide bands can feel tighter. If between sizes, consider moving up by half a size for comfort.

What if my knuckle is larger than the base of my finger?

Choose the smallest size that passes the knuckle comfortably. A comfort-fit or slightly rounded band profile can help.

Are ring sizes unisex?

Yes. UK letters and US numbers apply to everyone. Fit depends on finger shape and band width, not gender.

Are printable ring size charts accurate?

They can be close, but printer scaling may skew results. Confirm with callipers or a metal ring sizer for accuracy.

Is the string method accurate?

Acceptable for a first estimate, but string can stretch and be too thick. Use a narrow paper strip and confirm with callipers.

Can a ring be resized, and by how much?

In many cases a skilled jeweller can adjust a ring by one to three sizes. The exact range depends on the design, metal and stone setting. Full eternity bands, patterned shanks and heat sensitive details are often more limited. Ask for an assessment before any work is done.

Can antique or vintage rings be resized safely?

Often yes with a skilled jeweller, but pieces with enamel, patterned shanks or full eternity settings may be unsuitable. Assessment is recommended.

Do different countries use different ring size systems?

Yes. UK uses letters, US uses numbers, EU commonly uses inner circumference in millimetres, and Japan uses numbers. The calculator converts between systems.