A free ring size calculator that measures your size at home, in US, UK, European, Italian and German sizes.
Find your ring size from a string or a ring that fits, in US, UK, European and more sizes.
Your numbers
Wrap a strip of paper around the base of your finger, mark where it meets, and measure the length flat.
Your result
Fill in the fields above to see your result.
Embed this tool on your site
Paste the code into any page: WordPress, Webflow, Squarespace, Ghost or plain HTML. It's free with the credit under it, which links back to navid.me.
This free ring size calculator finds your ring size from a strip of paper around your finger, or from a ring that already fits, in US, UK, European, Italian and German sizes.
It draws your ring and marks your size on a full chart.
I built it because a ring bought online in the wrong size means a return or a resize, and the conversion charts on jewelers' sites often disagree. This one follows the published standards, so you can check its math.
Here's how to measure, a worked example, and why the same finger can be 2 sizes.
TL;DRKey takeaways
What is a ring size calculator?
A ring size calculator turns a measurement of your finger, or of a ring, into the ring sizes each country uses.
Every system measures the same thing, the inside of the ring, but each counts it differently. Europe uses mm around, the US a number scale, the UK letters.
How to measure your ring size
You need a strip of paper or a ring that fits, and a ruler.
A strip that's too loose over the knuckle is the size to buy, since the ring has to get on.
A worked example
Here's the example the calculator loads when you press Try an example: a finger 54.4 mm around.
That's 54.4 ÷ π = 17.3 mm across. In US sizes, (54.4 − 36.5) ÷ 2.55 = 7.0, a size 7.
In UK letters, (54.4 − 40) ÷ 1.25 = 11.5 steps above C, which lands on N½. Europe's size is 54.5, and Italy's is 14.
- UK and Australia
- J½
- Europe (ISO)
- 49.5
- Inside diameter
- 15.7 mm
- UK and Australia
- L½
- Europe (ISO)
- 52
- Inside diameter
- 16.5 mm
- UK and Australia
- N½
- Europe (ISO)
- 54.5
- Inside diameter
- 17.3 mm
- UK and Australia
- P½
- Europe (ISO)
- 57
- Inside diameter
- 18.1 mm
- UK and Australia
- R½
- Europe (ISO)
- 59.5
- Inside diameter
- 18.9 mm
- UK and Australia
- T½
- Europe (ISO)
- 62
- Inside diameter
- 19.7 mm
Why the same finger can be 2 sizes
Fingers change through the day and the year.
Warmth and time of day
Fingers swell in heat and after exercise, and shrink in the cold. Measure in the evening, when they're at their biggest.
Wide bands
A band over about 6 mm wide fits tighter than a thin one. Many jewelers suggest going up a half size.
Knuckles
If your knuckle is much wider than the base of your finger, size for the knuckle, or the ring won't go on.
Mistakes to avoid
These are the ways a home measurement goes wrong.
- Using string, which stretches, instead of paper
- Measuring a cold finger in the morning
- Measuring the outside of a ring instead of the inside
- Trusting a size from another country's chart without converting it
For a size you already know in one system, the ring size converter turns it into the others.
Who is the ring size calculator for?
It's for anyone buying a ring online or abroad, and these tools help around it.
- Ring size converter – for a size you already know
- Shoe size calculator – for your shoe size from your foot
- Currency converter – for a price in another currency
- Card fees abroad calculator – for what your card adds to a foreign shop
- Discount calculator – for the price after a sale
Measure twice, at the end of the day, and order with confidence.
Plan your money with your AI
Take your numbers further in
Ring Size Calculator FAQs
Questions about the ring size calculator? Here's what to know.
A ring size calculator turns a finger or ring measurement into ring sizes.
This free one gives US, UK, European, Italian and German sizes from a paper strip or a ring that fits.
Wrap a thin strip of paper around the base of your finger, mark where it meets, and measure the length in mm.
Type that into the calculator.
Measure straight across the inside, from edge to edge, in mm.
The calculator multiplies it by π for the size.
A finger about 54 mm around is a US 7, a UK N½ and a European 54.
Europe's size is the mm itself.
Each full size adds about 2.55 mm around, or 0.81 mm across.
The published relation is C = 2.55 × size + 36.5 mm.
They're letters from A to Z, with half sizes between.
Size C is 40 mm around, and each letter adds 1.25 mm.
Japan, China and India use tables with no published formula, and they vary between sources.
I left them out rather than guess.
Many jewelers suggest a half size up for bands over about 6 mm wide.
Ask the shop, since their own fit decides it.
At the end of the day, at a normal temperature.
Fingers are a little bigger in the evening and in heat.
Yes, it's free with no sign-up.
It runs in your browser.
I did.
I'm Navid Moazzez, and I made the ring size calculator as one of my free tools on navid.me.
More about me.
Navid Moazzez
AI business strategist & AI OS builder
Navid Moazzez helps creators and founders master AI and build their own AI Operating System (AI OS) to automate their business and life.
Navid.me is reader-supported. When you buy through links on this site, I may earn an affiliate commission. Learn more.
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