Body mass index is a quick screening number that relates weight to height. It is used widely because it is cheap and easy to measure, not because it tells the whole story about health. This calculator works out your BMI from your weight and height, places it in the World Health Organization's adult categories and shows the weight range that corresponds to a BMI of 18.5 to 24.9 at your height.
Enter kilograms and centimeters, or pounds with feet and inches; the calculation stays in your browser. Please read the section on limitations: BMI is designed for adults and is a starting point for a conversation with a health professional, not a diagnosis.
What BMI is and how it is calculated
BMI is weight in kilograms divided by the square of height in meters, so its unit is kg/m². A person who weighs 70 kg and is 175 cm tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial units the calculator first converts pounds to kilograms (1 lb = 0.45359237 kg) and feet and inches to meters (1 in = 0.0254 m), then applies the same formula.
The WHO classification for adults groups BMI as follows: below 16 is severe thinness, 16 to under 17 moderate thinness, 17 to under 18.5 mild thinness, 18.5 to under 25 normal weight, 25 to under 30 overweight (pre-obese), 30 to under 35 obesity class I, 35 to under 40 obesity class II, and 40 or above obesity class III. These are the cut-offs this calculator uses.
Risk at a given BMI also varies between populations: a WHO expert consultation in 2004 concluded that many Asian populations have higher health risks at lower BMI values and suggested additional public health action points for them. This tool shows the standard international categories only.
When a BMI check is useful
A quick personal reference point
For a rough sense of where your weight sits relative to your height, BMI gives one number you can track over time and compare with general guidance.
Preparing for a health appointment
Clinicians often record BMI. Knowing yours in advance, along with your measured height and weight, makes it easier to ask informed questions about what it does and does not mean for you.
Forms, programmes and research
Some fitness programmes, insurance forms and questionnaires ask for BMI. The calculator converts units for you and reports one decimal place, as BMI is usually given.
Reading your result
After you enter a weight and height, the Result panel shows three things: Your BMI in kg/m², the WHO category, and Healthy weight for your height, which is the range of weights that would give a BMI from 18.5 to 24.9. A bar underneath marks your BMI on a scale from 15 to 40, with ticks at 18.5, 25 and 30 and the normal range shaded.
Example in imperial units: 180 lb at 5 ft 10 in is about 81.6 kg at 1.778 m, which gives a BMI of 25.8 and the category Overweight (pre-obese). The healthy range shown for that height is 128.9 to 173.5 lb. In metric, 70 kg at 175 cm gives 22.9, Normal weight, with a range of 56.7 to 76.3 kg.
To catch typos, the calculator only answers for heights from 50 to 272 cm and weights from 2 to 650 kg, or their imperial equivalents.
Как пользоваться инструментом
- Choose Metric (kg, cm) or Imperial (lb, ft, in) under Unit system.
- Type your weight in the Weight field.
- Type your height in centimeters, or in feet plus inches; the inches box can stay empty for a whole number of feet.
- Read Your BMI, the WHO category and the healthy weight range, then read the note below the result before drawing conclusions.
Limitations and who should not rely on BMI
- BMI is for adults aged 20 and over. Children and teenagers are assessed with BMI-for-age charts that account for growth and sex, which this calculator does not use.
- It is not meaningful during pregnancy or while breastfeeding, when weight changes for reasons unrelated to body fat.
- Athletes and very muscular people can be classed as overweight while carrying little fat, because BMI cannot tell muscle from fat. Older adults who have lost muscle can show a normal BMI with excess fat.
- BMI does not measure body fat, where fat is stored, fitness, blood pressure or any other marker of health. This tool is for general information and is not medical advice. Talk to a doctor or registered dietitian about your weight and health.