Calculate body fat percentage – how it works and what it means for your health

Body composition

Body composition describes what your body is made up of – fat, muscle, bone and body water. Measuring body composition gives a more detailed picture of health than weight or BMI on their own.

A healthy balance between fat mass and muscle mass is linked to a lower risk of conditions such as heart disease and type 2 diabetes. Where fat is stored in the body also matters. Fat that sits deep inside the abdomen, around the internal organs – known as visceral belly fat – is linked to insulin resistance, inflammation and hormonal changes that can affect how your metabolism works.

By looking at body composition and taking more than just weight or BMI into account, you can get a clearer understanding of how your body is actually doing.

Body fat percentage

Body fat percentage shows how much of your total body weight is made up of fat. The rest is what’s called fat-free mass – everything that isn’t fat, such as muscle, bones, organs and body water.

Body fat percentage differs between men and women. Women generally have a higher body fat percentage than men, largely due to hormonal differences and biological factors, including those linked to reproduction.

How do you calculate your body fat percentage?

Body fat percentage and body composition can be estimated in several different ways. The methods vary in accuracy, cost and how easy they are to access.

Body fat percentage calculators

One simple way to estimate body fat percentage is by using an online calculator. These usually give a rough estimate based on information such as height, weight and sometimes waist measurement.

These calculators can be useful for tracking changes over time, but the results should be taken with a pinch of salt, as they don’t provide exact measurements.

Body circumference measurements

Measuring body circumferences is another way to estimate body fat. This involves using a tape measure around areas such as the waist, neck and hips. It’s easy to do at home and can give a general idea of body composition, but the results aren’t fully reliable as there are many potential sources of error.

Bioelectrical impedance (BIA)

Bioelectrical impedance, often shortened to BIA, is used in many smart scales. A very small electrical signal is sent through the body, and the resistance is used to estimate body fat percentage.

BIA is convenient and widely available, but the results can be affected by factors such as hydration, recent food intake and the time of day. For that reason, it’s best used to follow trends over time rather than to determine exact values.

Skinfold measurements (calipers)

Skinfold measurement uses a special tool called a caliper to measure the thickness of skin and fat folds at different points on the body. When done correctly by someone experienced, it can give reasonable estimates, but it’s less reliable at higher levels of body fat and requires practice to get consistent results.

DEXA scans

In healthcare and research settings, more advanced methods are used to measure body composition. One of the most established is DEXA, which uses low-dose X-rays to measure fat mass, muscle mass and bone mass separately, and to show how fat is distributed around the body.

DEXA is very accurate and is often used as a reference method in research. However, it’s relatively expensive and requires specialist equipment, which means it’s mainly used in healthcare or research rather than for regular monitoring.

What is a “normal” body fat percentage?

Body fat includes both essential fat, which is needed for vital functions such as hormone production and protecting internal organs, and stored fat in fat tissue.

Biologically, women tend to have a higher body fat percentage than men, due to hormonal factors and reproductive biology. As we get older, body fat often increases while muscle mass gradually decreases.

There are no strict cut-offs for what counts as a “normal” body fat percentage, as it’s influenced by sex, age, genetics and lifestyle. As a general guideline, men often fall between around 10–20%, while women are usually between about 20–30%, depending on age and activity level.

Knowing your body fat percentage can provide useful insight into body composition and health, but it always needs to be interpreted in context and alongside other measurements.

What affects body fat?

How much body fat you have, and where it’s stored, is influenced by both genetics and lifestyle. Some people have an inherited tendency to store more fat, particularly around the abdomen, which can increase the risk of overweight, type 2 diabetes and heart disease. Genetics can also affect appetite regulation, metabolism and how easy or difficult it is to lose weight. That said, having a genetic risk doesn’t mean that health problems are inevitable.

Lifestyle factors such as diet, physical activity, sleep and stress management can all positively influence body composition and help reduce health risks over time.

Body fat percentage, BMI and health – how do they fit together?

BMI is often used as a first screening tool to assess health and is calculated using height and weight. However, BMI doesn’t show how weight is distributed in the body or the difference between fat mass and muscle mass. This means people with a lot of muscle can be incorrectly classified as overweight or obese. At the same time, some people with a BMI in the “normal” range may still have a high body fat percentage.

That’s why body fat percentage is a helpful complement to BMI, as it gives more insight into body composition. It can provide a more nuanced understanding of health than weight and height alone.

At the same time, body fat measurements also have limitations. Results should be interpreted with care and always as part of an overall assessment of health.

Is body fat percentage important when you want to lose weight?

When losing weight, changes in body fat percentage and preserving muscle mass are often more meaningful than changes in total weight alone. Someone may lose only a small amount of weight but still significantly improve their health if body fat decreases while muscle mass is maintained.

Weight loss isn’t just about the number on the scales, but about how body composition changes over time.

Smart scales and follow-up – how Yazen can help

To track changes in weight and body composition over time, digital scales can be a helpful support during treatment. Yazen works with Withings, who make smart scales that estimate body fat percentage, muscle mass and body water as well as weight, using bioelectrical impedance.

These measurements aren’t exact medical values, but they can offer useful insight into trends over time. Within Yazen, this data is used as a complement to medical follow-up and is always interpreted in context, rather than as isolated numbers. This helps both doctors and patients build a clearer overall picture of health and weight development over time.

Summary

Body fat percentage can provide valuable information about body composition, but it doesn’t define health on its own. To get a fair and meaningful picture, it always needs to be seen in context and alongside factors such as BMI, weight, lifestyle and other health markers.

A high level of body fat, particularly when fat is concentrated around the abdomen, is linked to a higher risk of heart disease, type 2 diabetes, certain cancers, high blood pressure and raised blood fats.

By taking a whole-person view and following changes in body composition over time, it becomes easier to understand your health and reduce the risk of future health problems.

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