Do You Know How Breast Size Impacts Your BMI?

Breast size impact on BMI

Your breast size impacts your BMI, but not necessarily in a manner that should worry you.  The Body Mass Index (BMI) is an approximate measure of your body’s fat derived from your body’s total weight and size.

Every woman is different in their breast weight and how much actual fat sit is in their breast. The average breast weighs about 1.5 pounds, but this can vary depending on the woman and her age. Understanding your breast’s impact on BMI can help you better understand what it means for your health and fitness goals.

Illustration of the Breast Size Impact on the Body Mass Index

To illustrate the BMI impact of breast size, let’s take two women with identical weights as an example. One is 5’3″ tall with an A-cup bra size, and the other is 5’6″ tall with a D-cup bra size.

BMI is genetically positively correlated with breast size. The larger the breasts, the larger the BMI tends to be.  Assuming breast densities are equal (click here for more information about breast density), the woman with a larger bra size carries naturally more fat from her breast than the woman with smaller bra size.

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But height and body mass need to be factored in: In our example, the lady with the most significant bra is also taller despite having the same weight. It means that – as a whole – her body fat percentage approximated by her BMI is healthier than the shorter lady exhibiting the same weight.

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When Should I Adjust my BMI Results to my Breast Size?

If you are concerned about whether your breast size may be impacting your BMI, calculate first your BMI on a proven BMI calculator such as

  • If your BMI result falls in the upper end of the healthy BMI range, you are “fine” even if you carry a higher than average amount of fat from your prominent large breast.
  • If your BMI result is within a healthy BMI range by only a tiny amount due to your large bra size (ex: your BMI is 20, but you have a D-bras size), you might be slightly underweight.

In short, knowing exactly how the BMI result needs to be adjusted to your breast size is only a relevant question if your BMI is within the healthy range by a tiny amount. In such a case, the official BMI cut-off may be less relevant and require minor adjustments due to a larger or smaller than average amount of “good fat” sitting in your breast.

What the Science Says About the Breast Size Impact on the BMI

For a deeper understanding of how breast size impacts the BMI, please refer to the scientific resources:

Breast Size Impact on BMI: 1 Simple Conclusion  

In some cases, your BMI result needs to be adjusted for context, as Asian people do with the so-called Asian BMI. However, knowing exactly how the BMI result needs to be adjusted to your breast size is only a relevant question if your BMI is close to a healthy BMI cut-off.

A few exceptions aside (such as being a professional athlete or a bodybuilder), a BMI result out of the healthy official cut-off is most likely an indication that you are not as fit as you should be regardless of your breast size. Nothing can replace detailed and professional advice from a medical professional. You also may want to talk to your doctor about whether or not you should be wearing bras with smaller cup sizes so that you’re carrying less weight in them. It would not solve excess or lack of body fat, but it could help reduce back pain from having heavy breasts!

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