You often hear "BMI" mentioned by doctors and in fitness talk. But what exactly is BMI, how is it calculated, and what does it tell you? This guide explains it simply — the BMI formula, the chart, and what your healthy weight should be.
BMI stands for Body Mass Index. It's a simple number that, based on your height and weight, tells you whether your weight is low, healthy, or high for your height. It gives an early indicator of health — but not the full picture (explained below).
The formula for BMI is very simple:
Example: if your weight is 70 kg and height is 1.75 m, then —
BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9
This falls in the "normal/healthy" category.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal / Healthy |
| 25 – 29.9 | Overweight |
| 30 and above | Obese |
Note: This is the general World Health Organization (WHO) chart. In some Asian countries including India, doctors use slightly lower thresholds (e.g. above 23 as overweight), because health risks have been observed at lower BMI here too.
BMI only looks at height and weight — it doesn't distinguish between muscle and fat. So a wrestler or gym-goer may have a high BMI while being fit. Similarly, a slim-looking person may have high body fat. So treat BMI as an early indicator, not a final verdict. For a proper assessment, see a doctor.
BMI is a quick and easy way to know whether your weight is in a healthy range. Some of its benefits:
Since BMI doesn't give the full picture, it's good to also look at these alongside it:
Looking at all these together gives a better picture of health than BMI alone.
According to WHO, a BMI between 18.5 and 24.9 is considered normal/healthy. In India, some doctors advise staying below 23.
Children and teens have separate "BMI-for-age" charts, because standards vary by their age and sex. The adult chart doesn't apply directly to them.
BMI is derived only from height and weight, while body fat percentage measures actual fat. They're different — BMI is a simple early indicator, body fat is more accurate.
No. BMI isn't as accurate for athletes, bodybuilders, pregnant women and the elderly. In such cases, a doctor's advice is better.
This article is for general information only, not medical advice. BMI is just an early indicator. For accurate information and assessment about your health, consult a qualified doctor.
Where fat sits matters as much as how much there is. A simple alternative that many clinicians now find more informative is waist divided by height.
The guideline is easy to remember: keep your waist under half your height.
| Height | Waist to stay under |
|---|---|
| 5'2" (157 cm) | 78 cm |
| 5'5" (165 cm) | 82 cm |
| 5'8" (173 cm) | 86 cm |
| 5'11" (180 cm) | 90 cm |
| 6'1" (185 cm) | 92 cm |
It takes thirty seconds with a tape measure and adds information BMI simply cannot capture, because abdominal fat carries more metabolic risk than fat elsewhere on the body.
A BMI outside the healthy band is a reason to have a conversation with a doctor, not a verdict on your health or a reason for self-criticism. If thinking about weight or food has started to feel distressing, that is worth mentioning to a GP — it is more common than most people realise and support helps.
Official sources: World Health Organization