BMI Calculator
Calculate your body mass index from height and weight, see the general adult category it falls into, and the weight range that corresponds to a BMI of 18.5–24.9 for your height.
Result
Enter your values and select Calculate to see the result.
How to use this calculator
- Choose metric or imperial units.
- Enter your height and weight.
- The result shows your BMI, the general adult category and the BMI 18.5–24.9 weight range for your height.
Formula
BMI = weight (kg) ÷ height (m)²
In imperial units this is equivalent to 703 × weight (lb) ÷ height (in)². The calculator converts imperial inputs to metric first.
World Health Organization adult categories:
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 and above: obesity (class I 30–34.9, class II 35–39.9, class III 40+)
Worked example
Metric
70 kg and 175 cm: 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9 (healthy weight range).
Imperial
160 lb and 5 ft 9 in (69 in): 703 × 160 ÷ 69² ≈ 23.6.
Assumptions and limitations
- BMI is a screening measure, not a diagnosis. It does not measure body fat directly or distinguish muscle from fat.
- It may overestimate fatness in muscular people and underestimate it in older adults.
- Some health organisations use lower thresholds for people of certain ethnic backgrounds.
- These categories apply to adults aged 18 and over who are not pregnant. Children and teenagers are assessed with age- and sex-specific growth charts.
- This tool does not provide medical advice. Speak to a health professional about your individual situation.
Frequently asked questions
Is BMI accurate?
BMI is a quick population-level screening tool. It correlates with body fat on average but can be misleading for individuals, for example very muscular athletes. Waist measurement and clinical assessment give a fuller picture.
Can I use this for my child?
No. For people under 18, BMI must be compared against age- and sex-specific growth charts, which this calculator does not do.