BMI is an estimate of body composition, based on weight and height. A moderate BMI for females is usually 18.5–24.9. People who know their weight and height can use a BMI calculator to work out their BMI.

Body mass index (BMI) measurements can help someone understand whether they are underweight or overweight. However, BMI for people assigned female at birth 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 people assigned female at birth may find useful for keeping track of their health.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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

A person can use this calculator to figure out 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:

BMIWeight standard
Below 18.5Underweight
18.5–24.9Normal weight
30.0 and higherObese
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Image credit: Medical News Today

As a measurement, BMI is easy and inexpensive to measure.

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:

While it correlates with body fat levels, BMI does not distinguish between the weight that comes from fat, muscle, and bone.

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

BMI and muscle

Muscle tissue is denser than fat tissue. This means that people with high levels of muscle may have a high body weight that classifies them as being overweight or having obesity, even if they have a low body fat percentage.

People with high levels of muscle mass and a high BMI result typically have a lower risk of death than those with a high BMI score and lower muscle mass.

However, the limitation of BMI to account for this may lead to complications in treatment and affect a person’s insurance.

BMI and body fat

A high body fat percentage has an adverse effect on health. People with a moderate BMI but a high percentage of body fat may have a higher risk of developing metabolic syndrome.

Metabolic syndrome is a collection of risk factors that increase the risk of heart disease and type 2 diabetes. These risk factors include high blood pressure, abdominal obesity and high fasting glucose levels.

BMI and age

Additionally, the body’s proportion of muscle, fat, and bone typically changes as people age. 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.

As a result, BMI calculations may be inaccurate for postmenopausal women, who may have high body fat percentages but maintain moderate BMI. In severe cases, this may lead a person to miss out on preventive treatments for obesity-related conditions.

Learn more about the limitations of using BMI here.

In addition to BMI, people assigned female at birth can use other methods to understand their weight, body composition, and risk for certain diseases.

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.

A 2021 study of 4754 people aged 40–80 years without diabetes at the start of the study found that waist circumference and BMI were both predictors of diabetes.

Waist-to-hip ratio (WHR)

This method also measures abdominal fat and can be a strong indicator of future health risks. However, some researchers claim that taking a person’s waist and hip circumference into consideration as separate figures provides a better assessment of health risk.

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

Diagnostic methods

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.
  • Skinfold measurements: During this test, a doctor will pinch folds of skin and measure their thickness. They will often repeat this at several sites on the body.

Learn more about calculating WHR and what the results mean.

Below are some commonly asked questions about BMI for women.

What is the ideal BMI for a woman?

According to the National Heart, Lung, and Blood Institute, the ideal BMI falls in the range of 18.5–24.9.

What is the ideal BMI for women by age?

Body mass index (BMI) measurements do not take into account a person’s sex. Therefore, it is not possible to suggest an ideal BMI for women according to their age. Rather, a woman’s ideal BMI is based on their weight and height.

What is the average weight for a 5′ 4″ female?

In the USA, the average weight of a female aged 20 and over is 170.8 pounds (lbs).

According to the National Heart, Lung, and Blood Institute, a healthy weight for a woman who is 5 ft 4 in tall ranges from 110 – 140 pounds (lbs).

BMI is one of the tools individuals can use to determine a person’s risk of certain diseases, such as diabetes, heart disease, and stroke.

However, BMI is an outdated measurement of overall health and does not take into account multiple physical variables such as muscle mass, age, and menopausal status.

Body fat percentage, bone density, and muscle mass can all 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.