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RingSizeConvert.com

Convert MM to Ring Size

Millimeters are the most precise unit for ring sizing — enter your measurement below and we'll match it to a standard size.

How would you like to find your size?

Measure the inside diameter of the ring — straight across the inner hole, not the outside of the band.

Lay the ring flat and measure straight across the inside edge.

Is your mm number a diameter or a circumference?

This is the single most common mix-up when converting a millimeter measurement.

  • Diameter is the straight-line width across the inside of an existing ring — typically 14-23mm for adult sizes. Use "I have a ring" above.
  • Circumference is the distance around a string or paper strip wrapped around your finger — typically 44-70mm for adult sizes. Use "I measured my finger" above.

What ring size is your millimeter measurement? (Quick answers)

Direct lookup for the most searched millimeter diameters and circumferences.

Inside Diameter (Existing Ring)

  • 16 mm: US size 5½ · UK size L · EU 50
  • 16.5 mm: US size 6 · UK size L½ · EU 52
  • 17 mm: US size 6½ · UK size N · EU 53
  • 17.3 mm: US size 7 · UK size N½ · EU 54
  • 18 mm: US size 7¾ · UK size P · EU 56
  • 18.2 mm: US size 8 · UK size P½ · EU 57
  • 19 mm: US size 9 · UK size R · EU 59

Inside Circumference (Finger Measurement)

  • 50 mm: US size 5¼ · UK size K½ · EU 50
  • 52 mm: US size 6 · UK size L½ · EU 52
  • 54 mm: US size 6¾ · UK size N · EU 54
  • 56 mm: US size 7½ · UK size P · EU 56
  • 58 mm: US size 8¼ · UK size Q½ · EU 58
  • 60 mm: US size 9¼ · UK size S · EU 60
  • 62 mm: US size 10 · UK size T½ · EU 62

Quick mm reference

Common sizes and their millimeter measurements, at a glance.

Common ring sizes in millimeters
US / CanadaUS, CA, MXUK / AustraliaUK, IE, AU, NZ, ZAEUEU, FR, AT, BE, DK, SE, NO, FIGermany / NetherlandsDE, NLTurkeyTRJapanJP, CN, KR, HK, SGIndia (BlueStone)INIndia (Jewelove)India (VowJewels)India (The Vedic Crystals)Diameter (mm)Circumference (mm)
US / CanadaUS, CA, MX4UK / AustraliaUK, IE, AU, NZ, ZAHEUEU, FR, AT, BE, DK, SE, NO, FI47Germany / NetherlandsDE, NL15TurkeyTR6.75JapanJP, CN, KR, HK, SG7India (BlueStone)IN6.75India (Jewelove)6.75India (VowJewels)6India (The Vedic Crystals)7Diameter (mm)14.88Circumference (mm)46.75
US / CanadaUS, CA, MX5UK / AustraliaUK, IE, AU, NZ, ZAJ½EUEU, FR, AT, BE, DK, SE, NO, FI49.5Germany / NetherlandsDE, NL15.5TurkeyTR9.32JapanJP, CN, KR, HK, SG9India (BlueStone)IN9.32India (Jewelove)9.32India (VowJewels)8India (The Vedic Crystals)9Diameter (mm)15.7Circumference (mm)49.32
US / CanadaUS, CA, MX6UK / AustraliaUK, IE, AU, NZ, ZAL½EUEU, FR, AT, BE, DK, SE, NO, FI52Germany / NetherlandsDE, NL16.5TurkeyTR11.87JapanJP, CN, KR, HK, SG11India (BlueStone)IN11.87India (Jewelove)11.87India (VowJewels)10India (The Vedic Crystals)11Diameter (mm)16.51Circumference (mm)51.87
US / CanadaUS, CA, MX7UK / AustraliaUK, IE, AU, NZ, ZAN½EUEU, FR, AT, BE, DK, SE, NO, FI54.5Germany / NetherlandsDE, NL17.5TurkeyTR14.41JapanJP, CN, KR, HK, SG14India (BlueStone)IN14.41India (Jewelove)14.41India (VowJewels)12India (The Vedic Crystals)13Diameter (mm)17.32Circumference (mm)54.41
US / CanadaUS, CA, MX8UK / AustraliaUK, IE, AU, NZ, ZAP½EUEU, FR, AT, BE, DK, SE, NO, FI57Germany / NetherlandsDE, NL18TurkeyTR16.99JapanJP, CN, KR, HK, SG16India (BlueStone)IN16.99India (Jewelove)16.99India (VowJewels)14India (The Vedic Crystals)15Diameter (mm)18.14Circumference (mm)56.99
US / CanadaUS, CA, MX9UK / AustraliaUK, IE, AU, NZ, ZAR½EUEU, FR, AT, BE, DK, SE, NO, FI59.5Germany / NetherlandsDE, NL19TurkeyTR19.53JapanJP, CN, KR, HK, SG18India (BlueStone)IN19.53India (Jewelove)19.53India (VowJewels)16India (The Vedic Crystals)17Diameter (mm)18.95Circumference (mm)59.53
US / CanadaUS, CA, MX10UK / AustraliaUK, IE, AU, NZ, ZAT½EUEU, FR, AT, BE, DK, SE, NO, FI62Germany / NetherlandsDE, NL20TurkeyTR22.08JapanJP, CN, KR, HK, SG20India (BlueStone)IN22.08India (Jewelove)22.08India (VowJewels)18India (The Vedic Crystals)19Diameter (mm)19.76Circumference (mm)62.08
US / CanadaUS, CA, MX11UK / AustraliaUK, IE, AU, NZ, ZAV½EUEU, FR, AT, BE, DK, SE, NO, FI64.5Germany / NetherlandsDE, NL20.5TurkeyTR24.62JapanJP, CN, KR, HK, SG23India (BlueStone)IN24.62India (Jewelove)24.62India (VowJewels)20India (The Vedic Crystals)21Diameter (mm)20.57Circumference (mm)64.62
US / CanadaUS, CA, MX12UK / AustraliaUK, IE, AU, NZ, ZAX½EUEU, FR, AT, BE, DK, SE, NO, FI67Germany / NetherlandsDE, NL21.5TurkeyTR27.2JapanJP, CN, KR, HK, SG25India (BlueStone)IN27.2India (Jewelove)27.2India (VowJewels)22India (The Vedic Crystals)23Diameter (mm)21.39Circumference (mm)67.2

Lower-confidence data — Japan, India (VowJewels), India (The Vedic Crystals) comes from a single published retailer source, or is known to drift by 1–2 sizes at the top of the range. Confirm with the retailer before ordering.

Rounded scale — Germany / Netherlands uses a coarser step than US half-sizes, so one value can cover two neighbouring US sizes. Check the millimeter columns when you need to tell them apart.

View the full ring size chart →

Frequently asked questions

What ring size is 17 mm inside diameter?

A 17.0 mm inside diameter corresponds to US ring size 6½, UK size N, European size 53, and Japanese size 13. If your measurement is 17.3 mm, that equals US size 7.

What ring size is 18 mm inside diameter?

An 18.0 mm inside diameter corresponds to US ring size 7¾, UK size P, and European size 56. A measurement of 18.2 mm corresponds to US size 8 (UK P½).

What size ring is 52 mm or 54 mm circumference?

A 52 mm finger circumference equals US ring size 6 (UK L½, EU 52). A 54 mm circumference equals US size 6¾–7 (UK N½, EU 54).

Is 16 mm a size 6 ring?

No. A 16.0 mm inside diameter is a US size 5½. A standard US size 6 measures 16.5 mm inside diameter (51.9 mm circumference).