Chastity Size Guide - Measuring For A Perfect Fit

Posted by Mistress Scarlett 02/09/2016 14 Comment(s) Chastity Guides,

Many chastity wearers try a number of devices until they find the perfect fit. It is therefore important and less costly to understand the size of your penis and the measurements of chastity devices. Chastity device sizes can be broadly broken into the following three categories.




Penis sizes vary in length quite considerably when fully erect. It is however important to know the length of your penis when you are soft. By soft I mean completely un-erect. Not the length when you are semi erect but your normal penis length when not aroused, not hot and not cold. As a general rule of thumb, you should look for a device which is 1/4 to 1/2 of an inch smaller than your soft penis size. This is because not all chastity devices are worn the full length of your penis. The smaller size allows for the ring mechanism. It is also important to consider what you are looking for from a chastity device. Are you looking for chastity device which can be worn for longer periods of time or are you looking for a device which is perhaps a tighter fit and will help you fulfil your fantasies whilst playing?


Ring Size


The second most important size is the size of the chastity ring. The ring attaches to the chastity device or cage and runs around the base of your testicles. The image below will help you understand how you can measure yourself to find the correct ring size. This size can be a little tricky to measure however fear not because all of our devices have spare rings available to ensure you can find the perfect fit. This measurement provides you with a circumference measurement. You need to convert this to find the diameter, which is the measurement our rings are available in. Here is a list of ring sizes and their equivlient circumference:-

chastity size guide


Ring Size Diameter - Circumference


Ring Size 38mm = Circumference of 119mm


Ring Size 41mm = Circumference of 129mm


Ring Size 47mm = Circumference of 148mm


Ring Size 50mm = Circumference of 157mm



Again you need to consider whether you are looking for a tight fit, or something a little more comfortable. It goes without saying that you don't want the ring to be so tight that it cuts off blood flow to your member. It must also not be too loose to allow you to escape and cheat. Many chastity wearers will try two or three chastity ring sizes before they find the perfect fit. Depending on the device you have we offer four types of spare rings in various sizes. Please contact us if you need any assistance.


Girth or Width


Most chastity devices are similar in girth. The girth is the measurement of the cage in which you insert your penis. Many chastity wearers do not really need to consider this measurement but if you are particularly thick then you may want to consider s custom made chastity device. However this is not the case for 95% of us. Most chastity devices provide a cage diameter. The chastity cage diameter is the measurement which relates to the girth (width) of your penis.


At Toys 4 Naughty Boys, we provide you all the sizes of our chastity devices and chastity cages on each product page. If you have any queries, or need any assistance at all we are here to help. We have been selling chastity devices for years and we are not prudish. Don't be shy we are sure it has been asked before, drop us a line with any queries you may have.

14 Comment(s)

10/11/2016, 02:26:12 PM

Could I have some help with ring fitting on your chastity devices please? Using your guide I measured about 200mm Since sizes end at 50mm, and I know I'm not massively well endowed, I therefore assume that either the guide, or my measuring technique, is way off.

Mistress Scarlett:
11/11/2016, 12:24:03 PM

200mm is the circumference measurement, you need to convert that to find the diameter and the appropriate ring size. 200mm is a big measurement, but I'd suggest you try a 50mm ring and see how that goes.

Aphrodite's slave:
01/05/2017, 02:31:23 PM

I'm a proud wearer of a t4nb device since some months and I had that same problem. I'm on the lower average, but when erect my penis base measure up to a diameter of 50mm. Anyway, your fully erect size is not the measurement you need. That because the device won't allow your penis to become fully erect, the base will not reach her biggest size too. At least, thats how my penis work. I purchased a device with a 47mm ring, even if measuring 50mm when fully erect, but still it wasn't small enough. Fact is that this ring kinda squeezes my cock when i wear it alone and I'm fully erect, but feel like a wide ring when I wear my device, so I'm going to orders a smaller measure soon. My suggestion is that you need at least half centimeter less than you measure when your cock is free. Hope this being useful to next customers (and maybe helps t4nb, which makes such good devices, to improve this size guide too)

Mistress Scarlett:
17/09/2017, 12:24:59 AM

Hi, thanks for the comments and we hope they really help other wearers. Everybody is slightly different in their sizing requirements and comfort level so its all about trying and finding what works best for you.

15/07/2017, 09:27:40 AM

I read the directions for measuring the circumference of my cock in mm but I didn't measure up to the ring size. Please explain in detail how to find it what's the math steps to getting the correct answer Sincerely Mattie

Mistress Scarlett:
17/09/2017, 12:29:24 AM

Hi Mattie, thanks for the comment, please send us an email and we can help you find the size you need.

16/08/2017, 08:14:02 AM

I'm running at 26cm circumference. That's like 260mm. I used the largest ring I own and I have blue balls. In the literal sense. This is frustrating. Any help!?

Mistress Scarlett:
17/09/2017, 12:28:50 AM

Hi Rob, 26cm seems a very large measurement, you are either a very very big boy or perhaps have made a mistake with the measurement. The circumference is the measurement around your ball sack. If you imagine a using your fingers to create a circle, the measurement is around the outside of that circle. Hope that helps.

Jack sinclair:
30/01/2018, 11:15:24 PM

I have had a few different chastity devices but struggle with the fact I have one ball. Cub smaller than the other. The small one often slips back through the ring and then whole thing becomes loose. I’ve tried a smaller ring but it causes too much discomfort and swelling. What can I do?

jon grom:
09/04/2018, 01:34:52 PM

Please can you tell me when a 57 mm size F ring size for a "Confined" chastity device will be available? I've just received the device, with a 51 mm ring, which seemed appropriate, given your recommended measurement method. Although comfortable enough now I've finally managed to attach it, I found it almost impossible to attach, given that, though I'm into most to forms of BDSM and am very stoic, I don't enjoy pain when felt as such, especially on my genitalia, and certainly no pleasure when self- or accidentally-inflicted. Indeed, so difficult was it to don my device without impossible-to-endure pinching of the skin (as it always is with my more complex "The Vice" kind) that it would be impossible for me to allow anyone else to attach it, which thereby removes a major hoped-for very erotic pleasure, for both me and a partner. The problem that I hope a wider ring may solve is that my scrotal skin is so bunched up that it may allow that to be contained within the lower part of the ring, rather than becoming trapped around the sides as the main part is attached, thereby almost always becoming severely pinched, often yelp-making if the rods are finally suddenly click into place, there being no spare space for controlled attachment. I should add that I'm most impressed by the quality of the design and construction, and that it connects and disconnected perfect smoothly and without difficulty when not on my genitalia. I don't believe it's faulty; just too small for the insertion process (but just right once securely in place). A further problem that I have with this (and my other device) is that, though my penis is pretty well average in length and girth, whether erect or flaccid, I have great difficulty inserting it properly. Do you have any advice how best to do this, with minimal pain or discomfort in the process? Unfortunately, though I suffer from ED, the thought of attaching such a device is so erotic that my penis typically becomes somewhat engorged, even if not always firm let alone erect. When this (otherwise problematic but most enjoyable effect) happens, it's impossible to insert it at all. But even when I manage to dismiss any erotic thoughts so my penis is maximal flaccid - a process that takes a good while and which in itself somewhat defeats the purpose! - it's then still extremely difficult to insert it into the main part, not to mention often somewhat painful because of a tendency to pinch because the then flaccid skin of my penis merely crumples up within the device, making it ever more fatter and therefore even more difficult to insert then more I push. Even now, after wearing the device for nearly 2 hours, now with (disappointingly) no erotic sensations of thoughts, my penis has still not fully relaxed, naturally, as I'd hoped, to best use the space available. Regards, jon grom PS. Since wrote the above, I've just been to the loo, and while there, with much difficulty and discomfort during the process (but again not once done), I've finally managed to coax the glans beyond the last of the 3 main rings of the main device, and into the end cage, so the tip is squashed firmly against the end, as I'm sure is intended. Like this - the first time I've even managed to get my penis properly enclosed and displayed in such a device - it all looks magnificent, to myself, and surely any of my fem-domme friends; a perfect fit all round, as if made to measure. Encouragingly, it's also starting to feel somewhat erotic - presumably because the tip is now in contact with the cage on all sides, thereby inevitably stimulated, at least from time to time as I move - but also because of the thought of how beautiful my genitalia is now displayed, should it be seen, and the erotic impossibility of orgasmic release. Even so, some of my penis skin is still trapped in lowers sections, yet painful to push forward. Hopefully you can assure me that this should become easier with time.

jon grom:
09/04/2018, 01:37:53 PM

I may have given the wrong email address in my previous message. Maybe I should have emailed directly (e.g too long and paragraph breaks have been lost).

Joshua Quinn:
03/05/2018, 10:38:45 AM

I need some help. Can we please chat over email?

Joshua Quinn:
05/05/2018, 08:32:30 AM

I need some help with finding out what size I need. Can you please email me at

14/12/2018, 05:14:05 PM

Need some help with sizing for a sub of mine. These are his sizes. 4.5inch length 4.5inch girth 28mm base of balls Any advice on best cage etc to get?

21/01/2019, 02:50:43 PM,

I need a cage for my sub but can’t find anything on your site that will fit. He’s 125mm long and 45mm wide when flaccid & not aroused. He need a 60mm base ring as anything less is too tight. Do you have anything suitable or do you make custome cages? Thanks Steph

Stephen king:
06/02/2019, 10:55:14 AM

Having measured round mymtesticles it appears im 7ins round what size ring would you reccomend for a cock cage

07/07/2019, 09:34:31 PM

I have the same question s Andrew. I'm basically hung average (alas), yet the circumference measure I get is a whopping 26 cm - well above any of the measurements you offer for the C-ring that goes around the testicles. From my experience with other guys, I don't think of myself as having particularly large nutsack or nut yet this is a measurement that's off your scale. I've tried taking a 15 cm piece of string and wrapping it around - and that's really tight!

Kevin Busic:
23/06/2020, 03:03:11 AM

Is there such a thing as a cock cage for a 6 inch fully soft penis? I need to know because I have a hopefully soon-to-be BBC master who requires I wear one. I've never worn one before because of my size. But, I always have a very prominent raging erection when I'm with BBC. It's usually always ignored, & I never touch it; but if I'm to be trained properly then this cannot be! So, will I be able to report good news to my anxious wanna-be master?

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