About Breast Forms

How to Choose and Fit a Breast Prosthesis and Bra

The Tool Shed offers a number of breast forms for trans women, cross-dressers, or anyone who is looking to enhance their gender expression. This article describes how to measure for a bra size, as well as tips on choosing a corresponding form/cup size of your preference.

Each style of breast prosthesis will fit differently depending on the style of bra you choose. Therefore, it is important to learn about bra size and take your own measurements so you can find a bra and prosthesis combo that works well for you!

Measuring to Find Your Bra Size

1. Take your under-bust measurement
Using a soft tape measure, measure around your rib cage just under the pectoral muscles where the natural breast tissue joins the body. This is your under-bust measurement. Be sure to keep the tape measure level with the floor when placing it around your body. Take a snug measurement. This number will be used to figure your bra band size.

[Please note that some manufacturer’s bra sizing guides will have you take a measurement across the topmost part of your chest, just under your armpits, to find your band size. While this measure can work well for some people, individuals with wide upper back muscles may find the under-armpit measure to be far less accurate than the under-bust.]

2. Use your under-bust measurement to find your bra band size
This part seems like it should be easy, but it is slightly complicated by the bra industry itself! Logic would say that your bra band size should equal your under-bust measurement. So, for example, if your under-bust measure is 36 inches, you would think your bra band size would be 36… but it turns out to be not so simple!

For many years, the bra industry has used a bra band sizing system that recommends you add 4 to your under-bust measurement to find your band size. Many bra companies use a sizing system such that a person measuring 36 inches under-bust would wear a 40 bra band (36 plus 4).

Transform is a company that uses the "plus 4" system, so if you are buying a Transform See-Thru Bra from our site, use your measurement plus 4 to find your band size in that bra.

If you are buying bras from other companies
The "plus 4" rule described above for band sizing is pretty common in the industry, but in recent years it has fallen out of favor with some newer bra companies. There are a number of retailers who stock a much greater range of band and cup choices, especially for hard-to-fit sizes. Those more specialized retailers tend to rely on your physical measurement first, and then they will have their own sizing recommendations based on your under-bust measurement.

Confused? Don’t worry! The world of bra fitting is as much an art as a science. There are three important things to remember from all this. First: always know your actual under-bust measurement! Second: when shopping for a bra, ask if the style you are choosing uses a "plus 4" band sizing, or an actual measurement. If it is a decent shop, they should be able to help fit you based on their knowledge of the products. And third: whenever you can, try on a bra for fit, and know the return policy if you are buying bras online.

You might find a 36 band size works great in one brand, but that you wear a 38 in another company's bra. You'll also find that there are other elements aside from band band size that will make one brand or style fit your body better than another.

One more note on bra bands: they only come in even numbers. So, if you measure 35 inches, round up to 36 as your starting point for under-bust measurement.

3. Choose a Cup Size
Your band size number stays the same, no matter the size of your breasts. And with breast forms, you get to choose your cup size, or even try out different cup sizes by wearing different sized forms!

The size of the cups on a bra is indicated by a letter, starting with A and proceeding up the alphabet. Cup size A is smaller than B, B is smaller than C, C is smaller than D, and so on. There are sometimes double letters in the system, usually multiples of the letter D. DD is larger than D, and DDD is larger than DD. The odd exception to this system is AA, which is smaller than A!

Rather than being a fixed size or volume, cup size is relative to your band size. That is, a "B" cup on a very small person is actually smaller than a "B" cup on a very large person. The "B" refers to how far the breast tissue projects away from the body, not how big the actual cup is!

When choosing your cup size, consider your height, weight, and figure. Obviously, with breast forms you can choose from many different form sizes, but know that if you choose a cup size that is very large for a small frame, it may be harder to buy clothes that fit properly. Likewise, if you choose a cup size that is too small for your frame, your forms may not fill out your clothes. Women's clothing tends to be designed around "average" sizes, and when you fall outside those averages, proper fitting can be difficult.

If you know your usual dress size, use the chart below to find a suggested cup size. Everyone is different (and of course clothing sizes vary by brand), but the suggested sizes below are a great place to start for choosing your cup size.

Shirt Size Dress Size Suggested Cup Size
  0 A
SMALL 2 A
  4 A or B
  6 B
MEDIUM 8 B or C
  10 C
  12 C
LARGE 14 C or D
  16 D
X-LARGE 18 D or DD


After you choose your cup size, use the charts below to find the corresponding breast form size. Breast form sizes vary by style; see individual product descriptions to find which sizes are available in that form.

If you do not see your preferred breast form size in our stock, we are happy to arrange a special order of that size. Special orders generally take about a week to arrive in our store.

Bra/Breast Form Sizing Chart
To read this table:
Top row of numbers indicates bra band size (32 through 48).
Vertical column of letters (A through DD) indicates bra cup size.
Numbers in the rest of the table indicate corresponding breast form size. The form sizes indicated here should give you shallow-to-average cup fit. If you would like a fuller cup fit, try the form size just above. (Example: if you want a 36 C, you can try form sizes 5 and 6 to see which you prefer.)

Size Chart for Transform Brand Breast Forms

  32 34 36 38 40 42 44 46 48
A 1 2 3 4 5 6 7 8 9
B 2 3 4 5 6 7 8 9 10
C 3 4 5 6 7 8 9 10 11
D 4 5 6 7 8 9 10 11 12
DD 5 6 7 8 9 10 11 12  


Size Chart for Amolux Diamond Breast Forms

  34 36 38 40 42 44 46 48 50
A       4 4 6 8 10 12
B     4 4 6 8 10 12 14
C   4 6 6 8 10 12 14  
D 4 6 8 8 10 12 14    
DD 6 8 10 10 14 14      
E 8 10 12 14          



Size Chart for Aphrodite Breast Forms

  34 36 38 40 42 44 46 48
A   XS SM SM SM MD LG LG
B XS SM SM SM SM MD LG XL
C SM SM MD MD MD MD XL XXXL
D MD MD MD MD LG LG XL XXXL
DD MD MD LG LG LG LG XXXL  
E LG LG LG LG XL XL XXXL  
F LG LG XL XL XXXL XXXL    



How to Put Your Forms Into a Transform Pocket Bra
1. Spread the bra out on a flat surface with the inside of the bra facing you.
2. Hold the form by the edges with a flat hand so that the nipple is facing down.
3. Spread the elastic on the cup and slide the form in so that the nipple faces outward.
4. Adjust the form so it settles into the bottom of the cup.
5. Hold the bra up with the form inside the pocket to make sure it looks correct.
6. Be careful not to puncture the form or fold it. Transform silicone forms are very durable, but the polyurethane skin can be punctured.

How to Put Your Forms Into a Regular Bra
1. Put your bra on as you normally would, fastening the bra band comfortably.
2. Lengthen the bra strap on one side.
3. Pull the cup away from the chest wall.
4. Insert the form from the inside top of the cup. Turn the form in the direction that best fills the bra cup and looks the most natural. Repeat on the other side.
5. After forms are in place, adjust the straps on each side.
6. Look at the fit. Both sides should match and the bra cups should cover the prosthesis completely. The prosthesis top tapers should prevent clothing from sinking in. Each form should fill and not bulge at the top of the cup; plus, the forms should settle into the bottom of each cup. The straps should not cut into the shoulders.
7. If the forms are too big, too small, or do not fill where they need to fill, try another style or size of form.

Always be careful not to puncture the form or fold it when handling and fitting. Silicone forms are very durable, but the polyurethane skin on some forms can be punctured by sharp nails or rough handling. Never sleep in your breast forms unless the manufacturer indicates it is safe to do so—your body weight could cause the forms to rupture.