Your result will appear here
Fill in the fields and press Calculate.
Body mass index (BMI) reduces where your weight sits relative to your height to a single number: you divide your weight by the square of your height. Used by the World Health Organization, it marks the boundaries between underweight, overweight and obesity — but it is a screening tool, not a diagnosis.
Enter your weight and height, and your BMI, your category, and the healthy weight range for your height appear instantly.
How is it calculated?
Formula
BMI = weight (kg) ÷ height² (m). Remember to convert height from centimetres to metres: 180 cm = 1.80 m, squared is 3.24. So 82 kg / 3.24 = 25.3.
WHO categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal (healthy) |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (class 1) |
| 35.0 – 39.9 | Obese (class 2) |
| 40 and above | Severely obese (class 3) |
What BMI doesn't see
BMI can't tell muscle from fat. A muscular athlete may read "overweight," while someone with low muscle mass may look "normal" yet carry a high fat percentage. That's why BMI should be read alongside waist circumference and body fat percentage, not on its own — a waist-to-hip ratio calculator and a body fat calculator complete the picture. In children and pregnancy the adult BMI thresholds don't apply; percentile charts are used instead.
Finding your healthy weight range
Run the same formula in reverse: your height squared × 18.5 (lower bound) and × 24.9 (upper bound). For 1.80 m the healthy range is 59.9 – 80.7 kg. Where in that range you aim is personal; staying within it is what matters.
Worked example
Someone 1.80 m tall weighing 82 kg: BMI = 82 ÷ (1.80 × 1.80) = 82 ÷ 3.24 = 25.3. That value has just crossed the 25.0 threshold, so it sits right at the start of the "overweight" category. Since the healthy range for their height is 59.9 – 80.7 kg, they are 1.3 kg above the upper bound — dropping to 80 kg would move them into the normal range. Being that close to a boundary shows how a few kilos can change the category.
FAQ
How is BMI calculated?+
Divide your weight (kg) by the square of your height in metres: for 82 kg and 1.80 m, 82 ÷ 3.24 = 25.3. The tool lets you enter height in centimetres and converts it for you.
What is a normal BMI range?+
The WHO considers 18.5 – 24.9 normal (healthy). 25 and above is overweight, 30 and above is obese; below 18.5 is underweight.
Why can BMI be misleading for athletes?+
BMI can't distinguish muscle from fat, and muscle is heavy, so very muscular people can read "overweight." In that case waist circumference and body fat percentage are better indicators.
What is my ideal weight for my height?+
The healthy range is your height squared × 18.5 to × 24.9 (59.9 – 80.7 kg for 1.80 m). For a single "ideal" figure using the Devine formula, use an ideal weight calculator.
Can I use this to calculate my child's BMI?+
No — adult thresholds don't apply to children; they need age- and sex-specific percentile assessment. For infants, use a baby weight or baby height reference.
Does BMI alone tell me if I'm healthy?+
No, it is a screening tool. Blood values, waist circumference, muscle-fat distribution and lifestyle all matter; for a definitive assessment consult your doctor.