Ring Size Calculator – Convert Diameter & Circumference to US, UK, EU Sizes

Calculate My Ring Size

Enter one measurement — diameter OR circumference (in mm).

Inner Diameter (mm)

— or —

Inner Circumference (mm)

Your Ring Size Results

US / Canada

—

UK / Australia

—

EU / Denmark

—

Japan

—

Diameter

—

Circumference

—

Results match the nearest standard size in our verified chart.

How to Measure Your Ring

Measure an Existing Ring

Lay a ring on a ruler and measure the inside diameter (across the center opening) in millimeters. Enter this value above.

Measure Your Finger

Wrap a thin strip of paper snugly around your finger, mark where it meets, and measure the length in mm — that's your circumference.

Convert & Compare

Enter your measurement and click Calculate. Your US, UK, EU, and JP sizes will appear instantly.

💡 Tip: Measure your finger later in the day when fingers are at their natural size. Cold temperatures can make fingers up to one size smaller.

Prefer a visual method? Try our online ring sizer tool to match your ring directly against a calibrated on-screen circle.

For reference sizes by demographics, read our article on the average ring size for women.

Quick Reference

Common Ring Sizes at a Glance

The most frequently purchased ring sizes and their international equivalents.

Circumference (mm)	Diameter (mm)	US / CA	UK / AU	EU / DK	Japan
49.3	15.7	5	J	49	9
51.8	16.5	6	L	52	11
54.4	17.3	7	N	54	14
57.0	18.1	8	P	57	16
59.5	18.9	9	R	60	18
62.1	19.8	10	T	62	21

View the full ring size circumference chart →

FAQ

Calculator FAQs

What unit should I enter in the ring size calculator?

The calculator accepts measurements in millimeters (mm) only. If your measurement is in inches, multiply by 25.4 to convert to millimeters. For example, 0.68 inches × 25.4 = 17.3 mm.

Can I enter circumference instead of diameter?

Yes — the calculator accepts either the inner diameter or the inner circumference in millimeters. Enter the one you have measured and leave the other field blank. If both are entered, the diameter value takes priority.

How accurate is the ring size calculator?

The calculator matches your input to the nearest standard size in our verified international ring size chart. The accuracy of the result depends directly on how precisely you measure your finger or ring. For best results, use a proper ruler or caliper and measure multiple times.

What is the difference between EU and US ring sizes?

EU/DK ring sizes are numerically equivalent to the inner circumference in millimeters — for example, EU size 52 means the ring has a 52 mm inner circumference. US sizes use a different numeric scale where size 6 corresponds to approximately 51.8 mm circumference, and each half-size equals about 1.3 mm in circumference.