How to measure for a chastity cage

Choosing the right size is crucial for you, and we provide you with some measurement methods to help you. If you have any questions about measuring or purchasing, please feel free to contact us via email or social media.

Author: Ethan
Updated on: 2026.01.14

How to measure for the right size of chastity cage and ring?

Knowing how to measure yourself properly is crucial in order to select the appropriate size for your chastity cage and ring, and avoid any issues that may arise from an ill-fitting device. Our chastity cages come with a variety of ring sizes, and you can determine the best fit for yourself by measuring yourself accurately.

Before measuring yourself, it is important to understand the structure of the cage. All of our cages use a ball trap system which securely holds your testicles between the back ring and the cage to keep them in place.

Now that you have an overview of his structure, you need to make a few important measurements

1、Back ring – Internal diameter (inside width)

2、Cage length – Length of your flaccid penis

3、Internal Cage diameter – The internal width relates to your penis girth

How to measure the back ring

As I mentioned earlier, selecting the correct ring size for you is really important as a back ring that’s too small can cause you physical issues, which includes cutting off blood flow or the ability to urinate. Opting for a ring that’s too big will make it much easier to release yourself and will move around too easily, which could cause friction burns where the ring rubs against your skin.

To properly measure your ring size you’ll need the following items:

A piece of thick string or b) cotton piping cord measuring at least 12 inches in length. If you go for a cord try to find one that’s quite thick, ideally around the same thickness as the back ring you intend to buy, though one that’s slightly thinner will do fine. Neither should be stretchy and the material that you use needs to be rounded, not flat. Using a light material colour like white will make it easier to mark.

A black marker pen with a fine tip. This will be used later to mark the string or cord.

A flat 12 inch ruler.

Start measuring with a rope

Place the end of the string or cord on the top of your penis and wrap it around and under your testicles until it meets at the top again. Loosely make a knot where the material meets and test the string to make sure that it’s not too tight or loose. You can check this by seeing how easy it is to put your little finger under the string. It should only just fit under the string with some tension. If you can easily hold your finger under the string you’ll need to tighten the knot a bit, or loosen the knot if it’s much too tight. Leave it in place for five minutes. If you start to see any discolouration in your cock or balls then it’s cutting off blood flood and the knot will need to be loosened. If you’re able to, go to the toilet and try to urinate. If there’s no issue there either you’re good to move onto the next stage.

Tighten the knot in the string that you made earlier, but only do this when you’re completely flaccid. At this point it’s really important that you forget about it. I know, it’s much easier said than done. You’re excited and might get aroused thinking about the shiny new chastity device you’re measuring for, but it’s precisely this that you need to put out of your mind, for the time being at least. You need to get on with your day and forget all about it, unless any issues present themselves. If you start feeling the string digging into you and cutting off blood flow then it’s too tight, so very carefully release the knot and make the length slightly bigger. Tighten the string a little bit if it starts sliding down, but only a tiny bit at a time.

Friendly reminder

When measuring the size of the testicles, it is recommended to do so in a room with a comfortable temperature. Avoid environments that are too hot or too cold, as these conditions can affect the position of the scrotum and lead to inaccurate measurements.
Measure multiple times: Take measurements two to three times a day and use the average as a reference. This can help obtain a more accurate size.

Common mistakes

Incorrect measuring positions: Wrapping the measuring tape around the middle of the penis or below the testicles instead of at the base will result in inaccurate measurements.
Pulling too tight: Trying to forcibly reduce the size by pressing the tape against the skin will only make the ring too tight and restrict blood flow.
Measuring in extreme temperatures: After a hot bath or in a cold environment, the body reacts and changes shape. Especially in cold conditions, the testicles retract into the scrotum, which can make the measurement inaccurate.

Allow the body to adapt for a short period of time

Set an alarm for 15-20 minutes on your phone or ask your smart speaker to do it for you. This will give your body a little time to get used to it being tied around your cock and balls. If the alarm goes off after this amount of time and it feels comfortable then take your pen and mark the material at the edge of the knot. You can now cut the string at the point you marked it or untie it if you’re able to.
Place the length of string or cord along the flat ruler to get the ring circumference measurement. To get a more accurate measurement we recommend repeating this process at least 2 more times and at different times of the day. Due to temperature fluctuations over the duration of a day we’d suggest taking one in the morning, one at midday and one in the evening. This will give us 3 measurements that we can then divide by 3 to give you an average measurement.
Example: 141mm + 140.5mm + 142mm = 423.5 / 3 = 141mm
We can then take the average length measurement (in our example 141mm), which gives us the circumference. You then need to divide that by Pi (3.14):
Example: 141mm / 3.14 = 44.95mm
With that measurement you’ll have your ring size. Match that to the closest ring sizes available from our store.

Choose the right ring according to the size you measure

We don’t currently offer custom ring sizes unfortunately, so you’ll need to match up your measurements to the closest ring size that comes with the device you’d like. Some of our chastity kits come with a full range of ring sizes, so you’ll be able to experiment with the different sizes until you settle on the one that fits you the best. You can also change rings depending on the climate or temperature of the environment that you’re in.

Most of our stainless steel chastity cages come with one back ring, so we recommend measuring yourself properly. Be patient and do it right the first time. If you’re between sizes and would like to order a second ring with your device you can order a new back ring here.

Here are some top tips when you select your rings:

If you’re a beginner to chastity we recommend selecting the larger ring if you’re between sizes. For example, if you measure 48mm go for a 50mm ring instead of a 45mm ring. You can always buy a smaller 45mm ring from us later once you’ve become more used to wearing a chastity cage.
If the weather or your environment is slightly colder then your penis and scrotum will tighten, so opt for the bigger ring size.
When you’re in a warmer climate you’ll naturally be slightly larger, which is the best time to use a smaller back ring.

Don’t panic if you don’t get your ring size right the very first time. We’re here to help if you need a larger or smaller ring. Simply let us know and we’ll go through your options with you.

We have compiled some reference tables of back ring measurements in the table below

Length in mm	Length in inches	Size Birdlocked
119mm to 132mm	4.68 to 5.2 inches	∅40
133mm to 148mm	5.21 to 5.82 innches	∅45
149mm to 163mm	5.83 to 6.41 inches	∅50

Measuring the cage/tube internal diameter

This is super easy as we’ve already done something similar when taking the measurement for the back ring. Instead, we’re going to measure the girth or circumference of your penis.

Again, this measurement needs to be taken when you’re completely flaccid, so relax, focus

on something else that won’t get you aroused and follow these instructions:

Cut a length of thick white string and wrap it around your cock at its thickest point. We recommend doing this about half way up the shaft.
Mark the string with your pen being careful not to draw on your penis.
Place the length of string against your ruler to get the circumference.
Repeat the process and another 2 times at different points during a day. Add these measurements together then divide them by 3 to get your average girth.
Divide this measurement by 3.14 to give you the internal cage diameter.
Make a note of the number for when you select your cage.

Ideally you should fill as much of the cage as possible so that it fits like a glove. You don’t want to give yourself too much (if any) room for your cock to expand or grow into the cage, so have this in mind when making your selection.

Cage to snap ring gap

The Gap – The space between the cage and ring

With all ball lock chastity devices there’s a gap of varying size between the cage section and the back ring. This is known as “the gap”.

There’s a simple formula to work out if you should look for a wider or smaller gap:

High and Tight = Wider gap

Low and Loose = Smaller gap

Essentially if your testicles hang quite high up and are tight to your body you should look for a wider gap. If your balls hang low with plenty of skin making up your ball sack then you should look for a smaller gap to trap you between the cage and ring.

Over time as your body adjusts to long term chastity cage use it’s not uncommon for you to need a smaller gap. This is due to your balls starting to hang lower underneath the cage, which requires a smaller gap to keep you firmly in place.

Don’t go for a gap that’s too small as that can cause medical issues including cutting off blood flow. This is going to make you uncomfortable, which a well fitted cage shouldn’t do.

If you have any questions about the product or size, please contact us through the contact us page, we are happy to provide you with the best service.

Personal preference

Our size guide can only help you get started with using a chastity device, and it serves as a general reference. Your personal preferences may differ from ours. As long as you prioritize your health and safety, please remember that you should never feel pain or discomfort while wearing a chastity device. If you plan to wear it long-term, we recommend wearing it during the day and monitoring any changes, such as discoloration, loss of sensation, or unusual odors, to ensure the device fits properly.

FAQ

How to wear a chastity cage？

To wear a chastity cage, first pass the testicles and penis through the ring, then secure the penis with the main part of the cage, and finally lock the chastity device. For more tips and methods on wearing a chastity cage, please refer to the blog “How to Wear a Chastity Cage.“

What is the purpose of a chastity cage?

A chastity cage serves different purposes for different people. Originally, it was simply a tool to help control one’s desires. Over time, it gradually became associated with BDSM. For effeminate or cross-dressing individuals, wearing a chastity cage is often intended to better hide the penis and create a more feminine appearance.

How long can a chastity cage be worn?

If you are a beginner, it is not recommended to wear a chastity cage for long periods. You can wear it during playtime and observe whether any changes occur to the penis that might indicate a problem. For experienced users, long-term wear is possible, but it is important to maintain the cleanliness of the chastity cage. Failing to clean it regularly over extended periods can lead to bacterial growth and potentially cause health issues.

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