Ring size: What you should know before buying a ring online.

When you buy a ring online, you must ensure that you order the correct ring size  according to the supplier. Having a good look at the websites of many jewellery stores, we have noticed that there seems to be no accurate standard on which they all agree. It is therefore important that you know the exact size of your finger in millimeters by having it measured with an accurate gauge.

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Many websites offer a free ring sizer either made of plastic which they will send by post or a printable template which you can use yourself. Some will even tell you to use a piece of string, which we do not recommend as it is highly inaccurate. Another popular method is to measure the diameter of a ring that fits or compare it on a chart.

Using any of these methods is not the best way to determine the size of your fingers and should only be used as a rough guide. The only way to accurately find out the precise measurement is to get it done by a professional. Any reputable jewellery store on your local high street should provide this service free of charge. Most will not mind as it is an opportunity for a sale, even if you decide to buy a ring from somewhere else.

Buying your ring online

Once you know your size and find the ring that you wish to buy, check if the website provides precise measurements of their rings in millimeters. Inside circumference of the ring is the most accurate. If not, it’s a good idea to contact them in advance of your purchase, especially if the item is costly or you need the ring urgently.

Most good companies will provide a money back guarantee and/or a resizing service, but if you get it right at first there is no need to worry. It could be a costly experience as you may have to pay for shipping yourself. If none of these options are available, it’s best to start looking elsewhere unless you want to take the risk of receiving a ring that doesn’t fit.

Visit our Our Top 5 Online Ring Stores | A Great Selection of Rings from Ringmania.

Don’t trust a chart on any website

In addition, there are many examples of conversion charts online and you will find ours below. The problem with most is that they do not adhere to any kind of standard. Some are even copied from a rival company and not even checked for accuracy, just so the website can provide some information.

The charts that we have included here are only intended for you to convert your country’s standard to another which may help if you are unfamiliar with the difference in standards at particular websites.

What these charts won’t do is determine the size of your fingers and you must have them measured professionally as we have mentioned above.

Please bear in mind that the size of your finger will change according to factors such as temperature, change in weight or even time of the day. Unfortunately there is no magic solution and the only way to obtain an accurate measurement is to seek professional advice.

Not sure of your ring size? Use our International Ring Size Conversion Chart.

You will find that most ring sizes on this site are quoted using the UK standard system of A-Z (BS6820).

If you wish to find the equivalent size for your country, please use the conversion chart below.

There are several size standards which are currently in use depending on the country of origin. This can be confusing and we will attempt to explain the most common here.

  • There is a standard in Europe which defines the ring size in millimeters of the inner circumference: ISO 8653:2016. This European standard is used by Austria, France, Germany, Belgium and Scandinavia.
  • Italy, Spain, The Netherlands and Switzerland also use the ISO standard but subtract 40 mm from the measurement. Therefore a ring size 50 in France is equivalent to a size 10 in Spain.
  • A numerical scale is used in Canada and the United States with quarter and half sizes. Each full size is an increase of 2.55 mm in inside circumference. Size 0 = 36.5mm inner circumference or 1.437 inches.
  • In the UK, Ireland and Australia an alphabetical system is used with half sizes. It loosely corresponds with  the American system and is based on the old British standard BS6820 last issued in 1987. Each full size is an increase of 1.25 mm in inner circumference. Although the system has been replaced by BS EN 28653-1993 it is still in common use. Size A should have an internal circumference of 37.8mm or 1.488 inches.
  • Japan, China and most of South East Asia use only whole sizes from 1 to 27 which seem to have no correlation to diameter or circumference. However on closer inspection the sizes are actually based on diameter. An Asian size 1 has a diameter of 13 mm. Larger sizes are measured in steps of .333 mm.

It’s important to get an accurate measurement

Please note that the information on this page is intended as a general guide only. There are many conversion charts online at most ring suppliers. Unfortunately, none of then seem to agree and general standards are not commonplace.

We recommend that you check the exact ring size in millimeters before ordering as there are many variations. You should also have your finger measured by a professional jeweler unless you have access to an accurate set of ring gauges. For an approximate measurement, simply wrap a strip of paper around your finger, measure the length in millimeters at the overlap point. This measurement corresponds with Inner Circumference in the table below.


International Ring Size Conversion Chart

We have compiled this chart using information from the first ten websites which can be found in a Google search. As the figures can vary considerably between different versions, they may not be 100% accurate. Please check any ring size with the supplier before purchase. We have also compiled an additional chart (see update below) from measurements which are generally accepted as international standard.

Ring Size Conversion Chart

* Denotes nearest approximate size

The figures quoted above are accurate to the nearest tenth of a millimeter and will be suitable for most needs. However if you need a more precise measurement, the following formula can be used:

Inside circumference = (US Ring Size x 2.55) + 36.5

For the next quarter size add 0.6375

For the diameter (Measurement across the inside of the ring), you must divide the internal circumference by π (3.142)

Example: For a ring of UK size K the American equivalent quoted above is 5 1/4 (5.25).  Multiply 5.25×2.55 which is 13.3875. Add 36.5 and the inside circumference equals 49.8875mm

The inside diameter is 49.8875 ÷ 3.142 which equals 15.8776

ISO 8653:2016 is quoted as standard.

To determine the diameter of an Asian ring use the following formula:

(size minus 1) x 0.3334 + 13

Example: For a size 12 subtract 1 =11  multiply by 0.3334 =3.667 + 13 = 16.667 mm

As these measurements are so precise and would make very little significance in the measurement of a person’s fingers. The ring size is normally quoted to the nearest tenth of a millimeter.

If you prefer to know the measurement in inches, you should divide the size in millimeters by 25.4

*The sizes quoted above are intended as a guide only. We recommend that you double check the actual measurement with the supplier.


UPDATE 1st October 2018

Here is an updated and more accurate version of the above chart. Measurements are displayed to the nearest thousandth of a millimeter. More information will be added as required:

Ring Size Chart

Some useful information regarding International Ring Sizes

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I have been working in the fashion and jewellery industry since the mid 1970s when I started work in a seaside gift shop selling costume jewellery and fashion accessories. I worked for many years in the UK as a musician and electronics engineer and started my own business in 1995 as the owner of Ringmania.
After living in Phuket, Thailand for 15 years, I am now based in Sheffield UK since July 2019
Please contact me using the link below if you have any questions about Ringmania or any of our products/services.

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