BMI formula
Body Mass Index relates your weight to your height:
BMI = weight (kg) ÷ height (m)²
In imperial units the same result is BMI = 703 × weight (lb) ÷ height (in)². The calculator accepts either system and converts automatically, so you can enter 5 ft 7 in and 150 lb, or 170 cm and 68 kg, and get the same answer: 23.5.
Example: 165 cm and 65 kg → 65 ÷ (1.65 × 1.65) = 65 ÷ 2.7225 = 23.9.
Reading the result
The WHO ranges used by the coloured scale are:
| BMI | Category |
|---|---|
| below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
The marker on the bar shows exactly where you fall, and the “healthy weight” figure is the weight band that would give a BMI of 18.5 to 24.9 at your height. If you are outside it, the calculator also tells you how many kilograms or pounds separate you from the nearest edge, which is a more practical target than an abstract number.
Why Indian cut-offs are lower
Studies of South Asian populations show higher body-fat percentage and greater risk of type 2 diabetes and heart disease at the same BMI compared with European populations. The Indian consensus guidelines (ICMR and the Ministry of Health) therefore use 23 as the overweight threshold and 25 as the obesity threshold. If your BMI is between 23 and 25 you are “normal” by the WHO table but “overweight” by Indian guidelines; most Indian doctors will go by the latter. The calculator shows both so you can discuss it with your physician.
Limits of BMI
- It cannot tell muscle from fat. A 90 kg weightlifter at 180 cm has a BMI of 27.8 but may have very little body fat.
- It says nothing about where fat is stored. Abdominal fat is the greater risk, so a waist measurement above 90 cm for men or 80 cm for women (Indian cut-offs) matters even if BMI is normal.
- It is designed for adults. Children and teenagers are assessed with age- and sex-specific percentile charts, and BMI is not used during pregnancy.
- Older adults often fare better at slightly higher BMIs, and losing muscle with age can hide weight gain.
Using BMI sensibly
Treat BMI as a first check, not a verdict. If it is outside the normal band, or in the 23–25 zone, the next useful steps are a waist measurement, blood pressure, fasting glucose and lipid profile — all routine, inexpensive tests in India. Sustainable changes such as an extra 30 minutes of walking, cutting sugary drinks and keeping regular meal times move the number slowly and safely; aim for 0.5 kg a week at most.
Tips for accurate input
- Measure height without shoes, standing straight against a wall.
- Weigh yourself in the morning before eating, in light clothing, on the same scale each time.
- Use the imperial toggle if your gym or doctor records height in feet and inches; the fields carry values across when you switch.
Frequently asked questions
What is a healthy BMI?
The WHO classifies a BMI of 18.5–24.9 as normal. Some Indian guidelines use a lower overweight threshold of 23 because of higher cardiometabolic risk at the same BMI.
Is BMI accurate for everyone?
BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat, so athletes and older adults may be misclassified. Consult a doctor for a full assessment.