Introduction
This Ring Size Calculator tells you what ring size to buy. You only need one measurement: the distance around your finger, or the inside width of a ring you already wear.
Pick your method, type in your number in millimeters or inches, and the tool shows your US ring size right away. It also shows the matching size in the UK, Europe, Japan, India, France, Germany, Italy, and more, so you can shop from any store or website.
You also get the exact inner diameter and circumference for your size, a full size chart with your match marked, and a step-by-step look at the math. If your number falls between two sizes, the tool says so and helps you choose the better fit.
Use it before you buy a wedding band, an engagement ring, or a gift, so the ring fits the first time and you skip the cost of resizing. Once you know your size, a gold price calculator or sterling silver calculator can help you judge whether a band is fairly priced, and a discount calculator plus a sales tax calculator will tell you the real checkout total.
How to use our Ring Size Calculator
Tell us how you measured your finger and enter that number. The calculator then shows your US ring size, plus your finger circumference, inner diameter, international size conversions, a size chart, and a step-by-step solution.
Measurement Method: Pick String / Thread — Circumference if you wrapped a string or strip of paper around your finger and measured the length. Pick Existing Ring — Inner Diameter if you measured straight across the inside of a ring that already fits well.
Your Measurement: Type your number in the box. For the string method, enter the length of the wrap. For the ring method, enter the inside width of the ring. Decimals are fine, like 52.4.
Unit (mm or inches): Choose the unit that matches your ruler. If you switch units, the number you typed is changed for you, so you do not have to redo the math. If you want to check the conversion yourself, try our mm to inches calculator or the reverse inches to mm calculator.
Slider: Drag the slider instead of typing, or use your arrow keys for small steps. The box and the slider always match, and results update as you move.
Calculate button: Click it to see your ring size right away. Results also refresh on their own a moment after you stop typing.
Start Over button: Click it to clear your entry and go back to the default measurement in millimeters.
Ring Size: What It Means
A ring size is just a number for how big the inside of a ring is. It comes from two measurements:
- Inner circumference — the distance all the way around the inside of the band. This should match the distance around your finger.
- Inner diameter — the straight line across the inside of the ring, from edge to edge.
The two are linked by one simple rule: circumference = diameter × π (about 3.14). So if you know one, you know the other. A US size 6 ring, for example, has an inner diameter of 16.51 mm and an inner circumference of about 51.9 mm. If you want to see that formula on its own, our circumference calculator, diameter to circumference calculator, and general circle calculator all work the same way.
How to Measure Your Ring Size
There are two easy ways to do it at home:
- String or paper strip. Wrap a thin string, floss, or a strip of paper snugly around the base of your finger. Mark where the ends meet, then lay it flat on a ruler and read the length in millimeters. That number is your finger circumference.
- A ring you already own. Take a ring that fits that finger well, lay it flat, and measure straight across the inside from one inner edge to the other. That number is the inner diameter.
Millimeters give the best results because ring sizes are only about 0.8 mm apart in diameter. Even a small mistake can move you a full size. If your ruler is marked in centimeters, our cm to inches calculator can help you cross-check the reading.
Tips for an Accurate Fit
- Measure at the end of the day, when fingers are at their largest.
- Measure when your hands are warm. Cold fingers shrink and hot ones swell.
- Check your knuckle too. The ring must slide over it. If your knuckle is much bigger than the base of your finger, pick a size in between.
- Your dominant hand is often a half size bigger.
- Wide bands (6 mm or more) feel tighter, so go up a quarter or half size.
- Measure two or three times and use the average — our average calculator makes that quick.
Ring Sizes Around the World
Every country uses a different scale, but they all describe the same inside measurement. The US and Canada use numbers, often with quarter and half sizes. The UK, Australia, and South Africa use letters (A through Z and beyond). Europe and the ISO 8653 standard use the inner circumference in millimeters. Japan and China use their own number scale, and Germany and Switzerland often list the inner diameter in millimeters. That is why a US 6 is also a UK L½, an EU 52, and a Japan 12. Buying from an overseas shop? Check the price in your own money with our currency calculator, and if you are the one selling jewelry, the Etsy fee calculator and eBay fee calculator show what you keep after fees.
If You Land Between Two Sizes
Most jewelers say to round up to the larger size. A ring that is a little loose can be resized or held with a sizing bead, but a ring that will not slide over your knuckle cannot be worn at all. Keep in mind that rings with stones set all the way around (eternity bands) usually cannot be resized, so measure carefully before you buy.
Shopping for a wedding? Ring size is one line on a long list — our wedding alcohol calculator helps with the reception, and for other sized gifts the bra size calculator uses the same measure-first approach.