Most of these links go back to the reddit wiki. Here’s the source page this information came from. Due to lemmy.world not currently having a wiki we cannot make the same style wiki as the reddit. We also cannot link to sections so a lot of links go back to reddit, we tried to denote them in the post as Reddit or Lemmy.

Manual Sizing Guide

Things You Will Need:

• A Soft Measuring Tape (or a non-stretchy string/cord and ruler if you're desperate)
• Your Naked Boobs (NO BRA!)
• Pencil and Paper to Record Measurements

Part 1: The Measurements

When taking the 6 measurements indicated below, keep the following definitions in mind:

• Underbust – The line immediately below where your breast tissue attaches to your chest. (This may be covered by breast tissue if your breasts hang low)
• Bust – The line across your breasts at their fullest point. (This
  should be measured without distorting your breast tissue)

Refer to this image for a visual guide on how to take these 6 measurements.

Step 1. Loose underbust

Measure your underbust with the measuring tape loose
snug on your skin, being sure to keep it parallel to the ground.
(It should be on the verge of moving around and should not cut into your skin at all.)

Step 2. Snug underbust

Measure your underbust with the measuring tape comfortably
snug on your skin, being sure to keep it parallel to the ground. Aim for the tape to feel as snug as you would want a bra to feel.
(It should not be able to move around and should dig into your skin slightly).

Step 3. Tight underbust

Measure your underbust with the measuring tape pulled as
tightly as possible, being sure to keep it parallel to the ground.
(Breathe out as much as possible while taking this measurement.)

Step 4. Standing Bust

Measure your bust while standing, or sitting up straight, being sure to keep the
measuring tape parallel to the ground. The tape should be loose and not cut into your skin at all.

Step 5. Leaning Bust

Measure your bust while leaning over (so your face is looking at the
floor and your back is parallel to the ground), being sure to keep the
measuring tape straight. The tape should be loose and not cut into your skin at all.

Step 6. Lying Bust

Measure your bust while lying down on your back, being sure to keep the
measuring tape straight. You may find you need to to use a mirror or spotter for this measurement to ensure the tape is straight as possible. The tape should be loose and not cut into your skin at all.

NOTE: Again, your breast tissue should not be distorted while taking this measurement. This means the measuring tape should be in a circle around your breast tissue as it naturally falls while you are lying on your back.

Part 2: The Calculations

NOTE: The size you calculate is just a starting point. You will likely need to try on a
variety of sizes around what you calculate to find your perfect fit. Sizing can vary by
brands as well. Fit is also determined by the shape of the bra, so even if you have your
size correct, certain bras still may not fit perfectly. Please feel free to use our other
resources (including our experts) to determine your shape and what specific bras may
work for you!

This guide uses different methods for those who were assigned female at birth and those who were assigned male at birth.

If you are intersex, please post a [measurement check]

If you have measured in centimetres, please convert these to inches before continuing.

Step 7. Determine your band size.

Round your snug underbust (Step 2)
to the nearest EVEN whole number.

Example: Step 2 = 31.25” so band size = 32

NOTE: Band sizes only comes in even numbers. If your underbust measurement is closer to an odd number and you are unsure whether you should round up or down, keep the following in mind:

1. It is particularly common for smaller band sizes (32 and under) to need to size up for comfort. Try on bras with the cups on your back to determine band comfort alone. If you are uncomfortable, go up a band size.

2. It is also common for larger band sizes (36+) to need to size down, as the band has more material and stretches farther. Keep in mind bras should fit comfortably on the loosest hook when bought so they can be tightened as the material stretches.

3. If you have a difference of less than 2" between your snug underbust and tight underbust measurements, you may wish to size up in the band.

4. If you have a difference of 4" or more between your snug and tight underbust measurements, you may wish to size down in the band.

Step 8. Determine your initial cup size.

If you were assigned FEMALE at birth:

Is there a difference greater than 2.5”
between your Leaning bust measurement and Standing bust Measurement (Steps 5 and 4 respectively)?

IF YES: Average all three bust measurements by adding them together and dividing the result by 3. Use this number to calculate cup size.

IF NO: Use your leaning bust (Step 5) to calculate cup size.

If you were assigned MALE at birth:

Use a weighted average of all three bust measurements to calculate cup size.

Add together your Standing, Leaning and Lying bust measurement (Steps 4, 5, and 6), then add your Standing and Lying bust again (Steps 4 and 6). Divide this total by 5. Use this number to calculate cup size.

Subtract your loose underbust (Step 1 – the raw measurement, not the band size calculated in Step 7) from this number.

Find the difference on the following cup size chart to determine initial cup size. If your number is between two, count both cup sizes.

Cup Size Chart

NOTE: Please notice that this chart uses UK cup sizes. If you are in the US, it is still a good idea to go
by UK sizing (if you are in Australia or Europe, you may want to request additional help converting
your size). For smaller band sizes (sub-30) and larger cup sizes, most of the bras you will find will only
be made by UK brands anyway. In addition, US companies all have their own system, so it is difficult
to make a definitive chart. If you fall into a range that US companies carry and would like to buy from
them, be aware what system they use. You can check out this section of our Buying Guide on reddit for information on what system specific companies use. Another way is to count up from DD, as UK and US are the same to that point. For
example, if you are a UK FF, that is 3 cup sizes up from a DD. If the US brand you are looking at goes
DD → DDD → F → G, you would need a G cup in that brand.

Example A: Step 4 = 35”, Step 5 = 36.75”, Step 1 = 31.25”

Use leaning bust

36.75 – 31.25 = 5.5 = DD/E

Example B: Step 4 = 37”, Step 5 = 40”, Step 6 = 38.5", Step 1 = 31.5”

Use average (38.5)

38.5 – 31.5 = 7 = F

Step 9. Determine your final size.

Find the difference between your loose underbust (Step 1) and your calculated band size (Step 7), and round this to the nearest whole number. Then divide this by 2. We'll call this number "x".

Example A: Step 1 = 35.25", Step 7 = 34

Difference = 1.25" => 1

Divided by 2 = 0.5

x = 0.5

Example B: Step 1 = 30.5", Step 7 = 32

Difference = 1.5" => 2

Divided by 2 = 1

x = 1

If your loose underbust is smaller than your band size:

Decrease your cup size by x. This is your final cup size.

If your loose underbust is larger than your band size:

Increase your cup size by x. This is your final cup size.

Put your band size in front of your cup size and you have your complete bra size!

Example C: Step 1 = 42", Step 7 = 40, Step 8 = HH

As x = 1, and the loose underbust is larger than the band size, increasing the cup size by 1 gives J.

The Final size is 40J

Example D: Step 1 = 35.25", Step 7 = 34, Step 8 = FF

As x = 0.5, and the loose underbust is larger than the band size, increasing the cup size by half gives FF/G

The Final size is 34FF/G

Example E: Step 1 = 30.5", Step 7 = 32, Step 8 = C/D

As x = 1, and the loose underbust is smaller than the band size, decreasing the cup size by 1 gives B/C

The Final size is 32B/C

Example F: Step 1= 53", Step 7 = 50, Step 8 = DD/E

As x = 1.5, and the loose underbust is larger than the band size, increasing the cup size by one and a half gives F.

The Final size is 50F.

NOTE: We know what you’re thinking right now! “I can’t possibly be a __ cup!” This
thought is especially common among smaller chested people who, for instance, may have been
wearing around a 32B and now measure around a 28E. What most people don’t know
is that cup size is not static; there is no such thing as a “D cup” (or any other) by itself!
It depends on band size; 28E is a small size and is much smaller than a 36E. In addition,
you likely do not have all of your breast tissue sitting in the cup. When putting on a
bra, you should lean forward and scoop all the tissue that has been pushed under your
arms/on your back into the cups. Please do not disregard this guide because you think
it is impossible for you to be the cup size you receive.

NOTE: It is not unusual for this guide to provide multiple sizes. It is often
recommended to buy the same model of bra in a variety of sizes around what this
guide calculates. If none of them fit correctly, it is likely the wrong shape for you. Try a
variety of sizes in a different style until you become more familiar with what
size/shape works for you.

Additional Information

This is the end of our Sizing Guide. If you have additional questions, please refer to one of our sidebar guides for assistance:

• Beginners Guide – for a condensed version of the information available in our wiki.
• Fit Guide – for information regarding your new size, how bras should fit, and other miscellaneous fit questions
• Buying Guide on Reddit – for information regarding where to find bras in your new size and the different sizing systems used by different countries/brands.
• Shape Guide – for information about the different breast shapes, how to determine your own breast shape, and which bras work well for which shapes.
• General FAQ – for general and miscellaneous information that doesn’t fit well into our other guides
• Glossary – for terms about bras and breast anatomy

The above guides will likely be the most helpful for newer members, but feel free to look through the many other guides we have compiled to see if your question may fall under one of those categories.

If you cannot find the answer to your question in any of our guides, feel free to create a post and ask away!

Please Note: Each guide has a link back to it's reddit source at the top of the posts.

This guide and the measuring system involved were created by Reddit User /u/goodoldfreda in 2017 with data and help from the Reddit /r/ABraThatFits and the Reddit /r/AskTransgender community!

The previous measuring guide which we used for many years was created by Reddit user /u/shaytom with much help from the /r/ABraThatFits community. Revised in 2016 by /u/xuenylom to better align with the bra size calculator that /u/irisflame made.