BMI Calculator
Enter your height and weight to find your Body Mass Index (BMI), your weight category and the healthy weight range for your height. Works for adults aged 20 and over.
Result
- Category
- Normal weight
- Healthy weight range for your height
- 56.7 – 76.3 kg
- BMI Prime
- 0.91
- Ponderal index
- 13.1 kg/m³
What is BMI?
Body Mass Index (BMI) is a simple screening number that relates your weight to your height. It was devised by the Belgian statistician Adolphe Quetelet in the 19th century and is still the most widely used way to classify underweight, healthy weight, overweight and obesity in adults. It is quick and free to compute, which is why doctors, insurers and public health agencies use it as a first check.
BMI formula
BMI is weight divided by height squared:
Metric: BMI = weight (kg) ÷ height (m)²
US units: BMI = 703 × weight (lb) ÷ height (in)²
Example: a person who weighs 70 kg and is 175 cm tall has a height of 1.75 m. Height squared is 1.75 × 1.75 = 3.0625. BMI = 70 ÷ 3.0625 = 22.9, which falls in the normal-weight range.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 16 | Severe thinness |
| 16 – 16.9 | Moderate thinness |
| 17 – 18.4 | Mild thinness |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obese class I |
| 35 – 39.9 | Obese class II |
| 40 and above | Obese class III |
These are the World Health Organization cut-offs for adults of all ages and sexes. Some countries use lower thresholds for people of Asian descent (overweight from 23, obese from 27.5) because health risks rise at a lower BMI in those populations.
Healthy weight range
The calculator also shows the weight that would give a BMI of 18.5 to 24.9 at your height. Multiply your height in meters squared by 18.5 for the lower bound and by 24.9 for the upper bound. At 1.75 m that is 56.7 kg to 76.3 kg.
Limitations of BMI
- Muscle vs. fat: BMI cannot distinguish lean mass from fat, so athletes may be labelled overweight.
- Age: older adults tend to lose muscle, so the same BMI may hide more body fat.
- Fat distribution: abdominal fat carries more risk than fat on the hips, which BMI ignores. Waist circumference or a body fat estimate adds useful information.
- Pregnancy and children: adult BMI categories do not apply.
BMI is best used as a starting point. If your result is outside the normal range, a health professional can assess your overall risk using other measurements and your medical history.
Frequently asked questions
What is a healthy BMI?
For adults, a BMI between 18.5 and 24.9 is considered a healthy weight by the World Health Organization. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or above is classed as obese.
Is BMI accurate for athletes and very muscular people?
Not always. BMI only uses height and weight, so it cannot tell muscle from fat. A muscular person can have a high BMI while carrying little body fat. In that case a body fat measurement is a better guide.
Does the same BMI scale apply to children?
No. For children and teenagers aged 2 to 19, BMI is interpreted using age- and sex-specific percentile charts rather than the fixed adult cut-offs used by this calculator.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in meters squared. For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9. In US units, multiply your weight in pounds by 703 and divide by your height in inches squared.