How Big Will My Boobs Be?

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Many ladies wonder how big will their boobs be, especially if they are just starting puberty. Breasts develop at different ages and at different rates. It all depends on genetics. Each one of your breasts can have different proportions, too. I talk about how big your breasts can get in my article below.

How Big Will My Boobs Be?

In the United States, the average bra size is 34DD. In the U.K, however, it is 36DD. The size of your breasts can differ because of age, genetics and your weight.

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Breast size will also differ from one lady to another. The size of your breasts can change during your monthly period, during pregnancy, after giving birth and while breastfeeding.

What Determines the Size of My Breasts?

Listed below are the reasons why breast size is different from one women to the next.

Graphic image with a featured drawing of a woman wearing a matching blue undergarments while holding a yellow tape measure in her chest trying to determine her breast size

Factors That Determine Breast Size

FactorEffect on Breast Size
Family historyGenes influence hormone levels, which can then affect breast tissue
AgeBreasts grow during puberty
Body weightAn increase in body weight can increase body fat in the breasts
MenstruationBreasts grow as a response to increased progesterone and estrogen levels
Pregnancy and nursingProlactin promotes the growth of breast tissues called mammary alveoli

Family Background 

One thing that has the biggest contributions to the size of your breasts is your genetics. Your genes have lots to do with your characteristics, including the size of your breasts. 

However, just because your mom is a D cup does not guarantee that you’ll be one too. There are other factors that influence the size of your breasts.

Your Age

Your boobs may continue to grow or shrink depending on your age. Breasts start growing at puberty. Not all teens start developing breasts at the same time.

Breast growth depends on the amount of estrogen, a female hormone, you are producing. Your breasts can start growing at the age of 10 and typically stop growing once you are 18 to 20 years old.

As you get older, your breast tissues will begin to shrink because of tissue dehydration. Later on in life, your breasts will start to sag and get smaller.

Body Weight

Changes in your body weight can also affect the size of your breasts. Your breasts are made up mostly of fat tissues, so the more fatty tissues you have, the greater chance you’ll have bigger breasts and vice versa.

Your Period

Menstruating means having more hormones in your body. During your menstrual cycle, you may experience premenstrual syndrome (PMS) which includes pain in your lower abdomen and back, headaches, mood swings and tender swollen breasts that are painful to touch.

These symptoms are all because of the change in the amount of estrogen and progesterone in your body. These hormones can stimulate milk ducts making your breasts more tender and larger. After your period, your breasts will return to their normal size.

Pregnancy and Nursing

Pregnancy can cause massive breast size changes because of your hormones changing. These changes are the bodies way of preparing your breasts to nurse a baby.

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How to Determine Your Bra Size

Since not all breasts are created equal, it is very important to measure them to get your bra size. Having the right size of bra can keep your breasts healthy and in shape.

So here are the three parts that you should measure to know your size.

  • Measure the length around your torso with a tape measure. This measurement is called the band. 
  • Next, measure the length across your the fullest part of your breasts, which is commonly known as the bust.
  • Lastly, find the cup size of your breasts. Find the difference between the band measurement and the bust measurement. 1 inch difference equals an A cup, 2 inches equals a B cup, 3 inches equals a C cup and so on.

How Breasts Develop

Breast development is a natural process that occurs during puberty and continues throughout adulthood. During embryonic development, both males and females develop mammary ridges or milk lines that run along the chest wall, which contain cells that have the potential to develop into breasts. 

Hormonal changes, especially estrogen produced by the ovaries during puberty, stimulate the growth and development of this breast tissue. The first visible signs of breast development occur as small, firm lumps of breast buds that form beneath the nipples. 

These buds are composed of ducts, which are tiny tubes that will carry milk in the future. The ducts grow and branch out, spreading through the breast tissue. As breast development continues, fatty tissue accumulates around the ducts, causing the breasts to increase in size.

When Breast Development Begins and Ends

Breast development typically begins during puberty, usually between the ages of 8 and 13. The initial signs of breast development, such as the formation of breast buds beneath the nipples, often emerge as early as age 8 or 9.

On average, breast development peaks within three to five years after it begins. In most cases, breast development is completed by the late teens or early twenties, when the breasts have typically reached their adult size and shape. 

However, the breast size can continue to change throughout your life due to factors such as weight fluctuations, hormonal changes during the menstrual cycle, pregnancy, and breastfeeding.

What Is Considered to Be Normal Breast Size and Shape?

There is no specific definition or measurement for a normal breast size or shape, as breasts naturally vary depending on factors such as genetics, hormonal influences, body weight, and overall body composition. 

As a result, both small and large breast sizes can be considered normal and healthy. In the same way, different breast shapes can be considered normal, whether round, teardrop-shaped or asymmetrical. 

How to Make the Boops Grow

The growth of boobs is primarily determined by genetics and hormonal factors, and there are no guaranteed methods to make breasts grow beyond their natural potential. However, you can use the following natural tips to make your boobs look great.

  • Eat a well-balanced diet rich in nutrients to support overall body health, including breast tissue
  • Engage in regular physical activity to improve posture and muscle tone, which can enhance the appearance of your breasts
  • Wear a well-fitting bra to provide support to the breast tissues and enhance the appearance of your breasts
  • Maintain a healthy lifestyle by managing stress levels so you can maintain a good hormonal balance for optimal breast growth

Related Questions

Are There Conditions Associated With Breast Size?

Breast size can be influenced by conditions such as cysts, mastitis or inflammation. People with bigger breasts may also experience more tension and pain in the back, shoulders and neck.

Is It Normal for Breasts to Have Different Sizes and Weights?

It is normal for your breasts to have different sizes and weights because of hormonal imbalances and different growth rates. Although having uneven breasts can be unsightly, you can add padding or select a bra that is designed for uneven breast sizes.

How Do You Know When Your Breasts Are Fully Grown?

Typically, breasts reach full development between the ages of 17 and 18. The areolas and nipples should darken, and the breasts should become more rounded when fully mature.

Bra Size Measurement & Cup Size | A, B, C, D, DD Bra Sizes AND Extra Large Breasts


Breasts come in all shapes and sizes. The cup sizes range from AAA all the way to ZZZ, though the most common sizes are A, B, C, and D. Breast size is determined by your genetics, hormones, age, weight and other factors.

Curious about how big your breasts will be? Take this quiz below to get an idea!


Allena is the Founder and Editor of The Better Fit, a platform dedicated to empowering women with practical advice on bras and fitness, inspired by her own revelation of the widespread issue of incorrect bra sizing. Her expertise and tips have been recognized by major publications such as Cosmopolitan, Better Homes & Gardens, Insider, and NBC, making her a trusted voice in women's wellness and lifestyle.