BMI Calculator
Enter your height and weight to get your body mass index, the World Health Organization category it falls into, and the weight range that would put you in the middle of the healthy band.
What BMI actually measures
Body mass index is weight in kilograms divided by the square of height in metres. It was designed to describe populations rather than individuals, and it survives because it needs only two numbers anyone can measure at home.
Because height is squared, small differences in height move the result a lot. Never compare a BMI without the height it came from, and never apply adult categories to children.
Where BMI stops being useful
BMI cannot separate muscle from fat. A trained athlete at 1.80 m and 95 kg has a BMI of 29.3 — “overweight” — while carrying perhaps 12% body fat. Someone with low muscle mass can sit inside the healthy band while carrying a high proportion of fat.
It also says nothing about where fat is stored. Visceral fat around the organs carries more risk than fat on the hips, which is why waist-to-height ratio (keep the waist under half your height) is a useful companion measure.
WHO categories for adults
| BMI | Category | Interpretation |
|---|---|---|
| Below 16.0 | Severe thinness | Significant underweight, medical review advised |
| 16.0 – 18.4 | Underweight | Below the healthy band |
| 18.5 – 24.9 | Normal weight | Healthy band for most adults |
| 25.0 – 29.9 | Overweight | Increased metabolic risk |
| 30.0 – 34.9 | Obesity class I | Moderate risk |
| 35.0 – 39.9 | Obesity class II | High risk |
| 40.0 and above | Obesity class III | Very high risk |
Several countries apply lower cut-offs for people of Asian descent, where cardiometabolic risk rises earlier: overweight from 23 and obesity from 25. The calculator reports the WHO values, which are the most widely cited.
The healthy range shown with your result is simply the weight span that corresponds to a BMI of 18.5 to 24.9 at your height. Treat the edges as guidelines, not boundaries — a person at 25.2 is not in a different health category from one at 24.8.
Frequently asked questions
What are the WHO BMI categories?
Under 16 severe thinness, 16–18.4 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30–34.9 obesity class I, 35–39.9 class II, 40 and above class III.
How accurate is BMI for children?
Not at all with adult categories. Under 18, BMI is read against age- and sex-specific percentile charts that follow growth spurts.
What is a healthy BMI?
For most adults the WHO defines 18.5 to 24.9 as normal. Some countries use 23 as the upper limit for people of Asian descent because metabolic risk rises earlier.
Is BMI accurate for athletes?
No. It cannot separate muscle from fat, so muscular people are often classed as overweight. Body fat percentage or waist circumference is more accurate.
How do I convert BMI between metric and imperial?
Metric: kg ÷ m². Imperial: 703 × pounds ÷ inches². Both give the same number; 703 converts the units.
Can I use BMI while pregnant?
No. Pregnancy changes weight and body composition by design; antenatal care uses pre-pregnancy BMI and gestational weight-gain guidance instead.