Ring Size Calculator
Take a ring measurement and get the closest size in US, UK, European and Japanese systems, with the band width allowance and a mandrel check.
At a glance
- What you enter
- Inside diameter of the finger or ring, Band width, Metal, This is a hot shop or production run
- What you get
- US size, UK letter position, European size, Japanese size, Mandrel diameter to form on
- Formula shown
- Yes, every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only, always verify with a professional or official source before acting on them.
How to use the Ring Size Calculator
- 1 Enter Inside diameter of the finger or ring (mm), Measure across the widest point of a ring that fits, with calipers if you have them.
- 2 Enter Band width (mm), A band of 4 mm or more fits more snugly than a narrow one at the same size.
- 3 Enter Metal, Used for the spring back allowance in the mandrel check.
- 4 Enter This is a hot shop or production run, Uses the tighter end of the mandrel allowance for a fast, consistent result.
- 5 Press Calculate. You get US size, UK letter position, European size, Japanese size, Mandrel diameter to form on, and every intermediate step stays visible under "How is this calculated?"
- 6 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
A US 7 ring in a 4 mm band
An inside diameter of 17.3 millimetres, a 4 millimetre band in sterling silver.
You enter
- Inside diameter of the finger or ring
- 17.30 mm
- Band width
- 4 mm
- Metal
- 1
- This is a hot shop or production run
- No
You get
- US size
- 7.03
- UK letter position
- 13
- European size
- 54
- Japanese size
- 13.90
- Mandrel diameter to form on
- 16.80 mm
US 7, UK N, European 54, and a mandrel around 16.8 millimetres for sterling silver.
A wide 8 mm band
An inside diameter of 17.3 millimetres on a heavy 8 millimetre band.
You enter
- Inside diameter of the finger or ring
- 17.30 mm
- Band width
- 8 mm
- Metal
- 1
- This is a hot shop or production run
- No
You get
- US size
- 7.32
- UK letter position
- 14
- European size
- 55
- Japanese size
- 14.62
- Mandrel diameter to form on
- 16.80 mm
The band allowance lifts the effective measurement, so a wide band in the same size feels tighter.
Fine band in 14 karat gold
A slim 2 millimetre band with an inside diameter of 15.7 millimetres.
You enter
- Inside diameter of the finger or ring
- 15.70 mm
- Band width
- 2 mm
- Metal
- 3
- This is a hot shop or production run
- No
You get
- US size
- 5.05
- UK letter position
- 9
- European size
- 49
- Japanese size
- 9.10
- Mandrel diameter to form on
- 15.35 mm
Gold springs back differently from silver, so the mandrel figure changes with the metal.
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