Body weight alone has limited meaning. Two people with the same weight can differ significantly in body composition, fat distribution and metabolism. For this reason, medicine and nutritional science use various measurements to better assess health risks. The best-known are the body mass index (BMI), waist circumference and body fat percentage. Each of these values has strengths and weaknesses – and only in combination do they provide a realistic picture.
The Body Mass Index (BMI): A Classic with Limitations
The BMI is the most commonly used reference value for assessing the ratio of body weight to height. It can be calculated using a simple formula.
How to calculate your BMI
To calculate your BMI, divide your body weight in kilograms by your height in metres squared:
- Formula: BMI = body weight (kg) ÷ height (m)²
- Example: 70 kg ÷ (1.70 m × 1.70 m) = 24.2
The World Health Organization (WHO) uses the following classification for adults:
- Below 18.5: underweight
- 18.5 to 24.9: normal weight
- 25.0 to 29.9: overweight
- 30.0 and above: obesity (various grades)
Where the BMI reaches its limits
The BMI does not distinguish between muscle and fat mass. Physically active people with a lot of muscle can mathematically fall into the "overweight" range without being at health risk. Conversely, a normal BMI can give a false sense of security in people with little muscle mass and a high proportion of abdominal fat.
Age, sex, ethnicity and body build are also not taken into account. In older people, for instance, slightly higher BMI values are generally considered acceptable. The BMI is therefore a useful general reference for the population – but on its own, it is not sufficient for individual assessment.
Waist Circumference: An Indicator of Abdominal Fat
It is not so much the quantity but above all the distribution of body fat that influences health risk. In particular, so-called visceral fat – fat in the abdominal cavity surrounding the internal organs – is associated with an increased risk of cardiovascular disease, type 2 diabetes and certain metabolic disorders.
How to measure correctly
- Standing up, in the morning before breakfast
- Place the tape measure horizontally around the narrowest point between the lower rib and the iliac crest
- Do not pull in your stomach, breathe normally, and read the measurement at the end of a normal exhalation
WHO waist circumference thresholds
The waist circumference thresholds provide a good indication of whether health-relevant abdominal fat is present:
- Women: from 80 cm slightly increased, from 88 cm significantly increased risk
- Men: from 94 cm slightly increased, from 102 cm significantly increased risk
Waist circumference is simple, inexpensive and can be measured at home without any tools. Studies show that in many cases it correlates better with cardiovascular risk than BMI alone.
Waist-to-height ratio as a supplement
An additional reference value is the waist-to-height ratio. As a rule of thumb: your waist circumference should be less than half your height. This value is independent of sex and is considered practical for everyday use.
Body Fat Percentage: A Look Beneath the Surface
While BMI and waist circumference are indirect measures, measuring body fat percentage attempts to capture body composition more directly. It distinguishes between fat mass, muscle mass, water and bone.
Measuring body fat percentage – common methods
There are several ways to have your body fat percentage measured or to determine it yourself:
- Bioelectrical impedance analysis (BIA): A weak electrical current is passed through the body. Fat and muscle tissue conduct differently. Common in many body composition scales and in medical practices.
- Skinfold measurement (calliper): The thickness of skinfolds is measured at defined points on the body and used to estimate fat percentage.
- DEXA scan (dual-energy X-ray absorptiometry): A specialised X-ray method that distinguishes very accurately between fat, muscle and bone mass. Mostly used in medical settings.
- Hydrodensitometry and air displacement: Very precise, but rarely available in everyday life.
Reference values for body fat percentage
Values vary according to age and sex. As a rough guide for adults:
- Women: around 20–32% (depending on age)
- Men: around 10–22% (depending on age)
Values that are too low are just as unfavourable as those that are too high, as a certain amount of body fat is necessary for hormone balance and metabolism.
What you should keep in mind
Results from household scales using BIA technology in particular can fluctuate depending on fluid balance, time of day and manufacturer. However, they remain useful for tracking trends if performed under conditions that are as consistent as possible – for example, always in the morning, on an empty stomach and with an empty bladder.
So Which Value Is Meaningful?
The honest answer: no single measurement is enough to comprehensively assess individual health. Each parameter illuminates a different aspect:
- BMI: quick rough estimate of weight in relation to height
- Waist circumference: indication of health-relevant abdominal fat
- Body fat percentage: more detailed information on body composition
In medical practice, these values are usually combined and additionally related to laboratory values (blood sugar, blood lipids, blood pressure), lifestyle factors and family history. Only this overall picture allows a well-founded assessment.
Practical Recommendations for Everyday Life
- Always supplement the BMI with waist circumference – it is simple and informative.
- Pay less attention to individual snapshots and more to changes over time.
- Keep in mind that building muscle can cause weight to rise even though health is improving.
- Seek medical assessment if you have existing risk factors or notice significant changes.
- Avoid relying on a single value alone.
Conclusion
BMI, waist circumference and body fat percentage are not competing measurements but complement one another. The BMI provides a quick overview, waist circumference indicates the risk from abdominal fat, and body fat percentage gives more detailed insight into body composition. What matters is not the single number, but how it is interpreted in combination with lifestyle, laboratory values and personal well-being.
This article does not replace medical advice.