BMI calculator
Calculate your Body Mass Index (BMI) easily from your height and weight. The calculator instantly shows your BMI number and an approximate category (underweight, normal weight, overweight, obese). The calculation runs locally in your browser — no data is sent anywhere and no sign-up is required.
How the BMI calculator works
BMI (Body Mass Index) is a simple ratio that relates your weight to your height. It is calculated as weight in kilograms divided by the square of height in metres:
BMI = weight (kg) / (height (m) × height (m))
You enter your height in centimetres and weight in kilograms; the tool converts the height to metres and plugs it into the formula. The resulting number is then placed into one of four bands based on the World Health Organization (WHO) classification:
| BMI | Category |
|---|---|
| below 18.5 | underweight |
| 18.5 – 24.9 | normal weight |
| 25.0 – 29.9 | overweight |
| 30.0 and above | obese |
BMI is only an approximate indicator. It does not distinguish between muscle and fat mass, nor does it account for fat distribution, sex, age or ethnicity. Athletes with a high proportion of muscle may score a high BMI without actually being overweight.
How to use the BMI calculator
- In the Height (cm) field, enter your height in centimetres (for example 175).
- In the Weight (kg) field, enter your current weight in kilograms (for example 70).
- The result recalculates instantly — the BMI field shows the number and the category appears next to it.
- To try a different scenario, simply overwrite the values; there is nothing to submit or confirm.
Example: for a height of 175 cm (i.e. 1.75 m) and a weight of 70 kg the calculation is 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9. This BMI falls into the „normal weight" band.
| Height | Weight | BMI | Category |
|---|---|---|---|
| 175 cm | 70 kg | 22.9 | normal weight |
| 180 cm | 95 kg | 29.3 | overweight |
| 160 cm | 45 kg | 17.6 | underweight |
What the BMI calculator is good for
BMI is the most widely used quick screening tool for estimating whether your weight sits in a healthy range relative to your height. Doctors, nutrition advisers and fitness apps use it as a first reference point. It is handy when you want to:
- quickly find out which weight category you roughly fall into;
- track changes over time — for example during weight loss or building muscle;
- get a starting number for a conversation with a doctor or dietitian.
Because height and weight are sensitive personal data, you will appreciate that the entire calculation runs directly in your browser. Nothing is sent to a server, stored in any database, and you do not need to enter an email or register. When you close the page, the data is gone.
However, BMI does not replace a professional assessment. If your result falls into the underweight or obese range, or if you are working towards health goals, consult a doctor. They will also consider other indicators such as waist circumference, fat-to-muscle ratio or blood tests, which BMI alone cannot capture.
FAQ
How is BMI calculated?
BMI is calculated as weight in kilograms divided by the square of height in metres: BMI = kg / m². So for 70 kg and a height of 1.75 m it comes out as 70 / 3.0625 = 22.9.
What BMI is healthy?
According to the WHO classification, a normal (healthy) weight corresponds to a BMI between 18.5 and 24.9. A lower value indicates underweight, 25 to 29.9 overweight, and 30 and above obesity. These are only indicative bands.
Does BMI apply the same to men and women?
The basic formula and category boundaries are identical for adult men and women. BMI does not factor in sex, so both calculate it the same way. A more precise body-composition assessment can, however, take sex and other factors into account.
Is BMI accurate for athletes and muscular people?
Not entirely. BMI does not distinguish muscle from fat, so very muscular people may have a high BMI without excess fat. For athletes it is better to add a body-fat percentage or waist-circumference measurement.
Does this calculator apply to children?
No. For children and adolescents, BMI is assessed using age- and sex-specific percentile charts, not the fixed adult thresholds. This calculator is intended for adults; for children, consult a paediatrician.
Is my height and weight sent to a server?
No. The entire calculation runs locally in your browser using JavaScript. The values you enter never leave your device, are not stored anywhere, and no registration is required.
Why did I get a different BMI than in another calculator?
The formula is universal; differences usually come from rounding or units. This calculator uses metric units (cm and kg) and rounds the result to one decimal place.
Does BMI replace a visit to the doctor?
No. BMI is only a quick indicative screen. Assessing your health requires a more comprehensive examination and a conversation with a doctor who will also consider other indicators.
Sources & standards
📅 Last updated: 11 July 2026