Mandrel & Gauge: A Beginner's Guide To Ring Sizing

February 19, 2021 9 min read

Mandrel & Gauge 


There's nothing more exciting than getting a new ring - and nothing more disappointing than discovering that it doesn't fit right. So, what can you do to make sure that your ring fits perfectly the first time?

Firstly, memorise the #1 rule of fashion: never trust standardised sizing! True standardisation between brands does not exist. You know how clothing fits differently depending on which brand you buy? So sometimes you'll find you wear a size 10 from Brand A, but in Brand B you need a Size 16?  That's a prime example. There are some basic country-wide standards, but they're not enforced at all, so every brand is a little bit different.

The same is true of rings. You may have heard of different country-based ring sizes - US, UK, EU, HK, and so on - but just like clothing, the exact measurements will alwaysvary from brand to brand. In addition to that, there is usually an acceptable margin for error of about 1mm built into that sizing. So, if a brand advertises that its Size O has an internal circumference of 55mm, then the actual ring you receive could be anywhere from 54mm to 56mm. That's generally okay if you're going based off your measurements, because you'll be getting a ring that's less than 1mm too large or too small, so it should still fit you. But, if you go exclusively off the ring sizes, then you could swiftly find yourself with a problem. 

Let's use an example to illustrate the point. Brand A lists their Size O as having an internal circumference of 54.5mm. Brand B lists their Size O as 55mm. That's not a big deal, right? Wrong. If you take into account the 1mm margin for error, then it's possible for someone to get a Brand A Size O that is actually 53.5mm, and a Brand B Size O that's 56mm. While both rings are technically the same size, the Brand B ring is going to be far too big for the person who fits the Brand A sizing. 

The only way to be 100% certain that your ring is going to fit right is if you go based on the actual numerical measurements of the ring. These are usually the inside circumference and inside diameter

The inside circumference of a ring is the distance around the innermost surface. This is the easiest measurement to get if you want to measure your finger. You can use a ring sizing gauge, ring sizing belt, or simply wrap a bit of string around your finger and then measure it.  

The inside diameter is the distance across the widest point of the ring. This is the easiest measurement to get if you have a ring that fits already. Simply lay it flat on a table and measure it with a ruler, or use a mandrel.  

Some brands provide you with both measurements in their size chart, but most favour one or the other.  Luckily, there's an easy way to convert one measurement into the other. Maths!

No, seriously. Remember back in maths class in school, where they made you learn pi and geometry and all that jazz? You finally have a use for those skills!  Yay!  Or, if school was way too long ago and you don't remember those formulas anymore, just use the handy calculator below. You're welcome. ;D

How To Use Ring Sizing Tools

If you want to get a little more accurate with your ring sizing, then the best way to go about that is to invest in a set of ring sizing tools, like the ones we have for sale here. There are lots of different types of tools available, and using them can be a bit of a mission, so let me walk you through it.


A mandrel is a tapered stick designed to hold circular items in place while you're working with them. In the case of ring sizing mandrels, they also have measurements and sizes printed on them, like a ruler. They come in plastic, aluminium, or sometimes steel. 

To use a mandrel, simply slide your ring onto the stick as far as it'll go, and then read the number closed to the bottom side of your ring.  

The type of mandrel you need will depend on your location, and what you want to use it for.  Plastic mandrels are great for personal, home crafting, and small business retail use, but if you're making your own rings then you'll probably want to invest in a metal one later on. The plastic ones are cheap and convenient, but they're not going to last as long or be as their metal counterparts. But, metal mandrels are significantly more expensive.

You should also consider what measurements you want on your mandrel.  Some mandrels come in inches, which won't do you much good if you're going to be working in metric. Most mandrels I've seen have four different numbers on them, so check the product details before you buy to make sure you're getting what you need. 

CK Swagworks mandrels come with the following:

  • Side A: US/Canadian Sizing & Hong Kong Sizing. 
  • Size B: Japanese Sizing & Inside Circumference (mm).

Here are some close-up photos to show you the different sizing in better detail:

Pro Trip:  It's quite common for stores to use standardised stock photos provided by the manufacturer, which may not always exactly match the finished product. Always check the text on the product before you make your purchase, to make sure you're getting exactly what you need. If you're not sure, ask first. Always better to be sure before you spend your hard-earned money, right?


The word "gauge" is a generic term that is used to describe all kinds of different measuring tools.  When you're talking about ring sizing gauges, it describes a set of small rings that are inscribed or printed with different sizes and measurements. 

Gauges are very handy for sizing rings, because you can simply put one on your finger like a ring to see how that size is going to fit. This is especially handy if your fingers are an unusual size or vary along the length. Not all fingers are a single size, after all. 

As you get older, it's common for your knuckle to be larger than the rest of your finger, which can make it hard to find rings that will fit. There are some other tools to help with that, but we'll talk about that later 

Much like mandrels, ring size gauges are available in a range of different colours, measurements, and materials. I personally find metal gauges less useful than plastic ones, but they can be a little easier to read sometimes. But, for home use, plastic is great. With many of them, you can even remove the rings from the hoop if you find it annoying having them all bunched together like that, which I find quite handy. 

Every gauge is different, so check before you buy. Our gauges come with the following:

  • Side A:  US/Canadian Sizing & UK/AU/NZ Sizing 
  • Side B: Inside Circumference (mm) & Internal Diameter (mm)

Here are some close-up photos to show you the different sizing in better detail:

Pro Trip:  Not sure whether you need a mandrel or a gauge?  Get both!  I frequently use them together as part of my day-to-day routine, and I'd be lost if I only had one or the other. You can never have too many tools! 

If you decide to get a plastic gauge set and have trouble seeing the letters, try using a permanent marker to make the letters stand out.  The plastic gauges generally have raised lettering because of the way they're made, so if you run the tip of the marker gently over the letters, you can apply a layer of ink just to the raised surfaces, which makes them stand out a lot better. Or, you could just make a mess like I did. Whoops! If you do, a little nail polish remover will take that right off, then you can try again. 

Ring Belts

I am personally not a fan of ring belts, but they are a tool that's available so let's talk about them. 

Ring belts are strips of plastic or hard rubber that have various ring sizes printed on them, with a little notch to help you thread them around your finger and find your size.  

They're generally very cheap to purchase, and their small profile makes them ideal for just slipping in the jewellery box or purse and forgetting about until you need them. But, most of them come printed with sizes rather than measurements. That means you'll run into the whole "sizes aren't standardised between brands" issue. But, there is a trick to getting one that uses actual measurements instead of sizing, so let me share it with you. 

Are you ready?  Brace yourself!  If you want to get a ring belt that shows actual measurements instead of arbitrary sizes... find one that's marketed as European Standard Sizes.  

"Wait, what?" you say. "Haven't you been lecturing us all this time notto rely on the standard sizing?"

Yes, and I absolutely, 100% stand by that!  But, now that I've drummed that into you enough times you won't forget it, I think it's safe to teach you the one exception to the rule. There is actually an international standard for ring sizing (ISO 8653:2016), but it's not widely used outside of Europe just yet. It should be, but it isn't. EU Size is, quite simply, the inside circumference in mm.  You'll recognise it because the numbers on the belt will start in the forties, and end in the seventies. We don't have any in stock just yet, but they're coming soon! 

Ring Size Adjusters

Okay, now you've learned how to get your correct ring size, so you won't have any trouble getting the right size in the future.  Awesome!  But, what if you already have a ring that's the wrong size?  Or what about those situations where your knuckle is bigger than your finger itself?  Or if you're the kind of person who swells up during That Time Of The Month, or while you're pregnant?

If your ring is too small, then there aren't many options aside from taking it to a jeweller and having it resized.  You can try using a steel mandrel and a rubber hammer to stretch your ring out, but honestly you're only going to get an extra half-size at best, and there's a good chance you're going to mess up your ring in the process. If you'd like to learn how to do that, there are tutorials on YouTube that walk you through it, but I strongly recommend just taking your ring to a jeweller if you value it at all. Better safe than sorry with something irreplaceable. 

Good news if your ring is too big, though! There are lots of options available to help with that. At the time of writing, I'm putting together a kit containing a variety of different tools, but it's not ready just yet. Let's have a look at the different tools available.

Coil-style adjusters are a fantastic temporary solution. They're made from PVC, silicone, rubber, and they're easy to apply - just wrap the coil around the base of your ring, and cut it to fit. Quick, convenient, waterproof, and easy to remove if you have to. We have these in stock now, available here.  

Another option is the stick-on pad. These ones generally come in large sheets and are made from thick silicone with an adhesive backing. Most of the ones I've seen come pre-cut in various thicknesses to make them easy to use, but you can also cut them to size if you need something a little different.

The plus side of this type is that you get a lot of bang for your buck. The coil style you can generally get 3-4 rings out of before you run out, but the pad style comes with a lot more. It's also more versatile since you can use it on bands of all thicknesses, and it's invisible.

The one real down side of the sticky pad is that they're not waterproof. If you plan to use this kind long-term, I recommend taking your ring off when you wash your hands, otherwise it'll lose its stick real fast. 

Still, the sticky pad makes up for it with convenience. We also have this kind in stock right now, available here

Fitted clip-ons are one of the newer options, which also have their benefits and their limitations. They generally don't require adhesive, which means that they're reusable, washable, and waterproof. The down side is that they only fit rings with very specific band sizes, and they can't be adjusted or trimmed to fit other sizes. We do not currently sell these individually, but they will be available in the ring sizing kit when it's available. 

Last but not least, I have heard of some creative souls using aquarium-grade silicone or even glue to add a little extra thickness to the band of their ring. I have not personally tried this, but I'd love to hear from anyone who has so I can expand this guide. Or, if you have any other ideas, send them our way! I'm curious to hear what you've tried, whether it worked or not. Thanks for reading!

About The Author

The above guide was written by author, artist, and entrepreneur, V. L. Dreyer.  It is supplied free of charge exclusively through CK Swagworks. Please DO NOT DUPLICATE without express written permission, but feel free to reference and/or link back to this guide in your own work. Thank you!

Products Mentioned In This Post

The Ultimate Ring Size Adjuster Kit

Coming Soon!

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