How BMI is worked out
Body mass index is your weight in kilograms divided by your height in metres squared. For 70 kg and 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9. If you enter pounds, feet and inches, the tool converts them first, using 1 lb = 0.4536 kg and 1 in = 2.54 cm.
WHO and Asia-Pacific cut-offs
| Category | WHO | Asia-Pacific |
|---|---|---|
| Underweight | below 18.5 | below 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 24.9 |
| Obese | 30 and above | 25 and above |
Research shows that people of South Asian, Chinese and some other Asian backgrounds tend to carry more body fat, and face a higher risk of type 2 diabetes and heart disease, at the same BMI as people of European background. For this reason the WHO Western Pacific office proposed lower cut-offs in 2000, and they are widely used in Pakistan, India and elsewhere in Asia. If your family comes from South Asia, the Asia-Pacific setting usually gives a more useful picture.
What BMI does not tell you
BMI is a quick screening number, not a measure of health. It does not separate muscle from fat, so athletes can score as overweight. It says nothing about where fat is stored; fat around the waist carries more risk. A waist measurement of more than half your height is a useful extra warning sign.
This calculator is for adults aged 18 and over. Children and teenagers need BMI-for-age charts, and BMI is not used in the usual way during pregnancy. The result is for information only. Talk to a doctor before making big changes to your diet or weight, especially if you have a long-term condition or take regular medicine.
Small, steady changes in eating, sleep and daily activity tend to move BMI more reliably than strict diets, and even a 5% drop in weight can improve blood pressure and blood sugar.