Ring Size Converter
Find the perfect fit. Convert between US numbers, UK letters, and millimeter measurements for wedding bands and engagement rings.
Ring Size Calculator
Visual Reference
Inner Circle Diameter
Pro Tip: Measure the inside of a ring you already own that fits well. Compare that diameter (mm) to the table.
Global Standards
We cover the 4 major systems: US/Canada (Numerical), UK/Australia (Alphabetical), Europe (ISO Circumference), and Japan.
Diameter vs Circumference
Don't mix them up! Diameter is the distance across the hole. Circumference is the distance around your finger.
Comfort Fit
Wide bands (over 6mm) fit tighter than thin bands. You may need to go up a half size for a wide wedding band.
Ring Sizing FAQs
How do I measure my ring size in mm?
The most accurate way is to measure the inside diameter of an existing ring in millimeters. Alternatively, wrap a non-stretchy string around your finger to find the circumference (e.g., 52mm circumference = EU Size 52).
What is a US size 7 in UK sizing?
A US Size 7 is approximately a UK Size 'N' or 'N½'. The inside diameter for this size is roughly 17.3mm.
What is the difference between US and UK ring sizes?
US sizes use numbers (e.g., 6, 7, 8) while UK sizes use letters (e.g., L, M, N). There is no direct math formula; you must use a conversion chart like this one.
Is European ring size the same as millimeters?
Yes, mostly. European (ISO) sizes usually correspond directly to the inner circumference in millimeters. So a size '52' ring has an inner circumference of 52mm.
Complete Your Lifestyle
View HubHow to Measure Ring Size at Home (The Accurate Way)
Don't guess the size. Learn 3 accurate methods to measure ring size at home, how to measure secretly for a surprise, and convert between US and UK sizes.
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