Body mass index (BMI) is an estimate of how moderate a person’s body weight is based on their height and weight. Doctors consider a healthy BMI for women to be 18.5–24.9. A BMI of 30 or above may indicate obesity.

BMI measurements can help someone understand whether they have underweight or overweight. However, BMI for women has some limitations, as it does not measure body fat specifically.

In this article, we provide a BMI calculator, discuss the pros and cons of BMI measurements, and explain some other methods that women may find useful for keeping track of their health.

A group of women with a range of BMI for women huddle during a basketball game.Share on Pinterest
While BMI can act as a general indicator of health, it does not measure body fat.

The Centers for Disease Control and Prevention (CDC) define BMI as “a person’s weight in kilograms divided by the square of their height in meters.”

A person can use this calculator to determine their BMI:

Once someone knows their BMI, they can find out where their measurement falls in the following standard weight categories from the National Heart, Lung, and Blood Institute:

Weight standardBMI
UnderweightBelow 18.5
Healthy weight18.5–24.9
Overweight25.0–29.9
Obese30.0 and higher

BMI is a useful tool for understanding where someone’s weight falls on the scale from underweight to overweight. It can also help people maintain a moderate weight, which can reduce their risk for:

If a person finds that their BMI is not in the “healthy” range, they can begin to make changes to their diet and lifestyle to reduce the risk of these and other conditions.

As a measurement, BMI has the following benefits:

  • it is easy to calculate at home using a scale and tape measure
  • it is inexpensive to measure
  • it has a strong correlation with body fat levels
  • a significant amount of research shows a link between BMI and health

While BMI can estimate whether a person’s weight is moderate, it has some limitations.

While it correlates with body fat levels, BMI does not distinguish between the weight that comes from fat, muscle, and bone. Therefore, someone who is muscular could have the same BMI as someone with overweight.

Additionally, the proportion of muscle, fat, and bone in the body typically changes as people age, especially among females. The average female loses roughly 13 pounds of muscle and bone between the ages of 25 and 65, while belly fat increases to four times its previous amount.

A 70-year-old female who still weighs what she did when she was 25 may, therefore, have a BMI that falls in the healthy range despite having a much larger percentage of body fat.

A high body fat percentage has an adverse effect on health. A 2014 study found that people with a “normal” BMI but a high percentage of body fat had a higher risk of developing metabolic syndrome. Those with excess fat around the belly had a higher risk of mortality.

In another study, researchers found that some postmenopausal women with a body fat percentage of 35%, which doctors consider a sign of obesity, were not in the “obese” category according to their BMI.

As such, BMI alone may be a misleading measurement of someone’s overall health, particularly for people who are very muscular, are peri- or postmenopausal, or have abdominal fat but are otherwise a moderate weight.

In addition to BMI, women can use other methods to understand their weight, body composition, and risk for certain diseases. According to the Harvard School of Health, these include:

Waist circumference

This method measures belly fat, which is a key indicator of someone’s risk for weight-related disease. People can measure the circumference of their waist using a soft tape measure.

Waist-to-hip ratio (WHR)

This method also measures abdominal fat. A person can calculate their WHR by dividing their waist measurement by the circumference of their hips. The World Health Organization (WHO) state that a WHR of 0.85 or below for women means that they have a low risk for weight-related disease.

Diagnostic tests that a doctor may perform include:

  • Densitometry: This involves a doctor measuring someone’s body weight while they are in water. The test compares their weight measurements on land to their measurements in water to calculate body fat percentage. Densitometry generally only takes place in a research setting.
  • Dual energy X-ray absorptiometry: X-rays move through fat, muscle, and bone at different rates, so this approach passes two low level X-rays through the body to calculate relative percentages.
  • Bioelectrical impedance (BIA): BIA estimates someone’s body fat percentage by passing a low level electric current through the body.
  • Isotope dilution: In this test, a person drinks water that contains isotopes and then provides samples of bodily fluids. These samples give a doctor information on the individual’s body composition.

Learn more about calculating WHR and what the results mean.

BMI is one of the tools that individuals and doctors can use to determine a person’s risk of certain diseases, such as diabetes, heart disease, and stroke. However, it has some drawbacks.

For women, body fat percentages change over time. As BMI does not measure body fat specifically, it may not provide someone with all the information that they need about their risk for these diseases.

BMI for women is still a convenient and useful tool for measuring overall body weight, but a person who wishes to track their health may benefit from combining BMI with other metrics, such as WHR.