What is BMI?
Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate whether you're in a healthy weight range. It's calculated as your weight in kilograms divided by the square of your height in metres.
BMI categories
- Below 18.5 — Underweight
- 18.5 – 24.9 — Normal (healthy)
- 25 – 29.9 — Overweight
- 30 and above — Obese
How to read your result
BMI is weight in kilograms divided by height in metres squared. Someone 1.70 m tall weighing 68 kg has a BMI of 68 ÷ (1.70 × 1.70) = 23.5, which sits in the healthy band.
The number is a screening tool, not a measurement of health. It cannot tell muscle from fat, does not account for where weight is carried, and was never designed to assess an individual — it came from population statistics. Two people with identical BMIs can be in very different health.
What BMI does not tell you
- Body composition. Athletes and anyone with high muscle mass often read as overweight while being perfectly healthy.
- Fat distribution. Waist circumference predicts health risk better than BMI, because weight carried around the middle behaves differently from weight elsewhere.
- Age and life stage. The standard categories are for adults. They do not apply to children, to pregnancy, or straightforwardly to older adults.
This calculator is a general reference, not medical advice. Any decision about your weight or health belongs with a doctor who can see the whole picture.
Frequently asked questions
Is BMI accurate for everyone?
BMI is a useful general guide but doesn't measure body fat directly. Very muscular people may have a high BMI while being healthy. Treat it as a starting point, not a diagnosis.
What's a healthy BMI?
A BMI between 18.5 and 24.9 is considered healthy for most adults. For some Asian populations, health risks can rise from around 23, so consult a doctor for personal advice.
Does BMI work the same for men and women?
The formula and the categories are the same, even though men and women differ in typical body composition. That is one of the reasons BMI is treated as a rough screen rather than a diagnosis.
What is a healthy weight range for my height?
It is the weight range that puts your BMI between 18.5 and 24.9, which the calculator shows alongside your result. It is a wide band on purpose — there is no single correct weight for a given height.
Should I use BMI for a child?
No, not with these categories. Children are assessed against age and sex percentile charts instead, because a growing body changes shape as well as size.