BMI Calculator — Metric and Imperial
Enter height and weight in centimetres and kilograms, or feet, inches and pounds, to get your BMI and its category. BMI is a quick screening figure used by doctors worldwide to flag possible weight-related health risks.
BMI Calculator
Body mass index, metric or imperial
How it works
- BMI = weight (kg) ÷ height (m)².
- Under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30+ obese.
- BMI ignores muscle mass and body composition — it is a screening figure, not a diagnosis.
- In imperial units: BMI = 703 × weight (lb) ÷ height (in)².
- Waist circumference is a useful complement: risk rises above 102 cm (men) or 88 cm (women).
Worked example: 78 kg at 1.80 m
- 1Square the height: 1.80 × 1.80 = 3.24.
- 2Divide weight by that: 78 ÷ 3.24 = 24.07.
- 324.07 sits in the 18.5–24.9 band, so the result is 'healthy weight'.
BMI 24.1 — healthy weight
BMI categories (adults, WHO)
| BMI | Category |
|---|---|
| Below 16.0 | Severely underweight |
| 16.0 – 18.4 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese class I |
| 35.0 – 39.9 | Obese class II |
| 40.0 and above | Obese class III |
Categories apply to adults. Children and teens use age- and sex-specific percentile charts.
Frequently asked questions
Is BMI accurate for everyone?
No. BMI does not distinguish muscle from fat and is less reliable for athletes, older adults, pregnant people and children. Treat it as a rough guide and speak to a doctor for personal advice.
What is a healthy BMI?
For most adults, 18.5 to 24.9 is classed as a healthy weight. Some guidelines use lower cut-offs for people of Asian descent, where health risks rise at lower BMI values.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. For 170 lb at 5 ft 10 in (70 in): 703 × 170 ÷ 4,900 = 24.4.
Why is my BMI high when I am muscular?
Muscle is denser than fat, so muscular people can score 'overweight' with low body fat. Waist measurement or body-fat percentage gives a better picture in that case.
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