When it comes to tracking weight loss and overall health, two metrics often come into play: body mass index (BMI) and body fat percentage. Both of these metrics are frequently mentioned in fitness and health circles, but they measure different aspects of your body composition, which can lead to confusion about which one is more important for your weight loss goals. Understanding the difference between these two metrics can help you make more informed decisions about your health and fitness journey.
What is Body Mass Index (BMI)?

Body mass index (BMI) is a widely used method of classifying individuals based on their weight relative to their height. was developed in the 19th century by Belgian mathematician Adolphe Quetelet and provides a quick overview of a person’s weight status, placing them into categories such as underweight, normal weight, overweight or obese.
To calculate BMI, divide weight in kilograms (kg) by height in meters (m) squared. For imperial units, BMI is calculated by dividing weight in pounds (lb) by height in inches (in) squared and multiplying by a conversion factor of 703. (Tip: There are many online calculators that can help you with this.)
For example, if you weigh 150 pounds and are 5 feet 6 inches tall, your BMI would be 24.2. A BMI of 24.2 would be place you in the “normal weight” category according to standard BMI ranges:
- Underweight: < 18.5
- Normal weight: 18.5 – 24.9
- Overweight: 25 – 29.9
- Obese: ≥ 30
While BMI is easy to calculate and useful for quick reference, it does not take into account the amount of weight that comes from muscle mass versus fat mass. Because of this, a person may be considered obese when they actually have an athletic, muscular build.
What is body fat percentage?


Body fat percentage refers to the proportion of your body weight that comes from fat. Unlike BMI, which doesn’t distinguish between fat and muscle, body fat percentage provides a more accurate picture of body composition, offering insight into how much of your body is fat versus lean mass (like muscle, bone, and organs).
There are several methods for measuring body fat percentage, ranging from the simplest to the most accurate:
- Skinfold forceps: This method involves pinching the skin at different locations on the body and measuring the thickness of the skinfold. These measurements are then used to estimate the overall body fat percentage.
- Bioelectrical Impedance Analysis (BIA): This method uses a weak electrical current passed through the body to estimate body fat. Because fat and muscle conduct electricity differently, the device can estimate body fat percentage.
- Dual-energy X-ray absorptiometry (DEXA): Often considered the “gold standard,” DEXA scans provide a detailed analysis of body composition, including fat, muscle and bone density.
- Hydrostatic weighing: This method measures body density by comparing a person’s weight on land with their weight underwater. It is very accurate but difficult for most people to access.
Main differences between BMI and body fat percentage


Although both BMI and body fat percentage provide insight into your health, they do so in different ways:
- What they measure: BMI is a simple calculation based on height and weight, while body fat percentage specifically measures the amount of fat in relation to total body weight.
- Precision: BMI does not distinguish between fat and muscle, meaning that a very muscular person can be classified as overweight or obese. Body fat percentage, however, gives a more accurate measure of body composition.
- Individual or collective use: BMI is more useful for population studies and screening, as it provides a rapid way to assess potential health risks in large groups. Percent body fat is more suitable for individual assessments, particularly when accurate body composition is essential.
Why Body Fat Percentage is More Important for Weight Loss


When it comes to weight loss and overall health, body fat percentage is often a more meaningful metric than BMI. Here’s why.
- Targeting Fat Loss: Weight loss should ideally come from fat, not muscle. By focusing on body fat percentage, you can ensure that your efforts are leading to fat loss, not just a lower number on the scale.
- Tracking progress: Body fat percentage can give you a better idea of your progress, especially if you’re also building muscle through exercise. Even if the scale doesn’t move much, a reduction in body fat percentage means you’re losing weight.
- Health consequences: A high percentage of body fat is associated with a higher risk of health problems such as heart disease, diabetes, and metabolic syndrome. Monitoring and reducing your body fat percentage can reduce these risks, even if your BMI is in the normal range.
In conclusion, while BMI can be a useful screening tool, it’s important to look beyond this number, especially if you’re serious about losing weight and improving your health. By focusing on reducing your body fat percentage rather than just lowering your BMI, you can achieve more significant and lasting results in your weight loss journey.
Gillean Barkyoumb, M.Sc., RDN
Gillean is a media dietitian with over a decade of experience working with brands across television, content creation and consulting. Learn more about Gillean
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