BMI Calculator
Height and weight in, BMI out — nothing leaves your browser. This is a starting reference point, not a diagnosis: it can't tell you your body composition, only where your BMI sits. If you want to understand what it means for you specifically, that's a conversation with Fredericka.
Enter your height and weight to see your BMI.
Below 18.5
Underweight
18.5 – 24.9
Healthy range
25.0 – 29.9
Overweight
30.0 and above
Obese
What is BMI?
BMI, or body mass index, is your weight in kilograms divided by your height in metres squared. Someone who is 1.65 m and 68 kg has a BMI of 25.0. It is a single number describing weight relative to height — nothing more than that, and it was never designed to describe an individual person.
What do the BMI categories mean?
The World Health Organization classifies adult BMI into four ranges. A BMI of 25 or above is defined as overweight, and 30 or above as obesity. These are the international cut-offs, and they are the same ones the calculator above uses.
| BMI | WHO classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy range |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
What can BMI not tell you?
It cannot tell you what your weight is made of. BMI uses total body weight, so it cannot separate muscle from fat, and it says nothing about where fat sits on your body — which is the part that matters most for metabolic risk. The WHO itself describes BMI as a surrogate marker of fatness and states that additional measurements, such as waist circumference, help in diagnosing obesity.
This is why the calculator above is labelled BMI and not body composition. True body composition — fat mass against lean mass — cannot be derived from height and weight, and any tool claiming otherwise is giving you a number that looks precise while measuring the wrong thing.
Does BMI work the same for everyone?
Not necessarily, and this is genuinely unsettled rather than something to state confidently either way. The relationship between BMI and actual body fat is known to vary between populations. A 1998 meta-analysis found that at the same body fat, age and sex, BMI differed substantially by ethnic group — Ethiopians by 4.6 kg/m² and American Blacks by 1.3 kg/m² below Caucasians. Other studies in African populations point in different directions, and the picture is not resolved.
Where the evidence has been strong enough to act on, WHO has said so explicitly. Its 2004 expert consultation kept the international cut-offs in place while identifying additional action points of 23.0 and 27.5 as population-specific guidance for Asian populations. No equivalent adjustment has been adopted as international guidance for African populations, so the standard cut-offs above remain what is used.
The practical version: treat your BMI as one reading, not a verdict. What it means for you depends on your body, your history, your labs and your symptoms — which is what a consultation is for.
Sources
- World Health Organization — Obesity and overweight fact sheetSource of the 25 and 30 cut-offs, and of the description of BMI as a surrogate marker of fatness.
- WHO Expert Consultation, “Appropriate body-mass index for Asian populations…”, The Lancet, 2004Retained the international cut-offs while identifying additional action points (23.0 and 27.5) for Asian populations.
- Deurenberg P, Yap M, van Staveren WA. “Body mass index and percent body fat: a meta analysis among different ethnic groups.” Int J Obes, 1998Reports that at the same body fat, age and sex, BMI differs by ethnic group — including Ethiopians at 4.6 kg/m² and American Blacks at 1.3 kg/m² below Caucasians.
