What is BMI?
Body Mass Index (BMI) is a simple screening measurement that estimates whether your weight is healthy for your height. It's calculated by dividing your weight by the square of your height, and is used worldwide by doctors, insurers, and fitness professionals as a quick first check — not a diagnosis. Because it only uses two numbers, BMI can't tell the difference between muscle and fat, which is why it works best as a starting point rather than the final word on your health.
How is BMI Calculated?
The formula is straightforward. In metric units: BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lbs) ÷ height (in)². For example, someone weighing 70 kg at 1.75 m would have a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — right in the middle of the "Normal weight" range. Our calculator does this instantly, and also converts freely between metric and imperial so you don't have to do the maths yourself.
BMI Categories & Chart
The World Health Organization defines four standard adult BMI categories:
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese | 30.0 and above |
These bands are what our color-coded bar above is based on, so you can see at a glance where your result sits.
BMI for Indian and Asian Adults — A Different Standard
Research from the WHO Asia-Pacific expert panel found that people of South and East Asian descent tend to carry more body fat at the same BMI compared to Western populations, and face higher health risk at lower thresholds. Because of this, many Indian health guidelines (including ICMR) recommend using lower cutoffs: overweight from a BMI of 23, and obese from 27, rather than the standard 25 and 30. If you're using this calculator as an Indian adult, it's worth mentally shifting the "Overweight" line down by about two points.
BMI for Men vs. Women
The BMI formula itself doesn't change between men and women, but its interpretation can. Women naturally carry a higher percentage of body fat than men at the same BMI, while men tend to carry more muscle mass — which is denser than fat and can push BMI higher without extra body fat. Neither effect is large enough to need a separate formula, but it's a useful reason not to over-interpret a single number.
Limitations of BMI
BMI doesn't distinguish between muscle and fat, doesn't account for age, bone density, or where fat is distributed on the body, and can misclassify very muscular people as "overweight." It also isn't designed for children, pregnant women, or the elderly. For a fuller picture, many clinicians pair BMI with a waist-to-height ratio or body fat percentage measurement.