Rings Sizer Find My Size
Free Tool

Measure an Existing Ring

Instant conversion from a ring you already own

How to measure a ring you already own

If you have a ring that already fits the finger you're sizing for, this is one of the most reliable home methods — there's no risk of pulling a string too tight or too loose. All you need is a ruler with millimeter markings.

  1. Lay the ring flat on a table with a ruler placed directly underneath it, or beside it, so you can read the scale clearly.
  2. Measure straight across the inside edge of the ring — from one inner wall to the opposite inner wall, through the center. This is the inside diameter, not the outside width of the band.
  3. Enter that number below to see it converted across every major sizing system.
US—
UK—
Japan—
EU / Ø mm—

A few things that affect accuracy

  • Make sure you're measuring the inside of the band, not the outside — the metal itself adds a millimeter or two to the outside width.
  • Wide bands (6mm+) tend to fit more snugly than a thin band at the same labeled size, so if this ring is unusually wide, you may want to size slightly differently for a new, thinner ring.
  • If the ring is oval or slightly warped from wear, measure at a couple of different angles and average the results.
  • Finger size also shifts a little with temperature and time of day, so keep that in mind if you're measuring for a different finger than the ring came from.

Don't have a ring to measure? Try the string or paper method instead.

See other methods
This gives a strong estimate based on standard sizing tables. For an engagement ring or anything hard to resize, confirming with a jeweler's metal ring gauge is worth the extra step.

Frequently asked questions

What if I don't have a ruler with millimeter markings?+

Toggle the unit switch above to inches and enter your measurement in inches instead — the tool converts it automatically. Most standard rulers show both, so check the opposite edge if you're not sure.

What if the ring is oval or slightly bent?+

Measure across a couple of different angles and use the average — a slightly warped ring can read a millimeter or so differently depending on where you measure, and averaging smooths that out for a more reliable result.

Does this method work for wide bands or eternity rings?+

Yes — the inside diameter measurement works the same regardless of band width. Just know that if you're buying a new, differently-sized wide band based on this reading, wide styles typically fit more snugly and may need sizing up slightly.

How accurate is measuring an existing ring compared to a jeweler's gauge?+

It's one of the more reliable home methods, typically within a fraction of a size, since there's no risk of pulling a string too tight the way there is with the string method. For anything expensive or difficult to resize, a jeweler's metal gauge still holds a tighter tolerance.

Can I use this to size a ring as a gift?+

Yes — borrowing a ring the person already wears on the correct finger and measuring it this way is one of the most accurate discreet sizing methods. Our engagement ring sizing guide covers this and a few other approaches for surprise purchases.

Related reading

How to measure your size Printable ring sizer Engagement ring sizing guide Sizing for wide bands Can a ring be resized? Does temperature affect finger size? How to size a ring for a child