BMI Calculator
Calculate your Body Mass Index from height and weight (metric or imperial) and see your WHO weight category instantly.
About the BMI Calculator
Body Mass Index (BMI) is a quick screening number that relates your weight to your height. This free BMI calculator supports both metric units (centimetres and kilograms) and imperial units (feet, inches and pounds), and instantly shows your BMI along with your weight category based on the World Health Organization classification: underweight, normal weight, overweight or obese.
The formula is simple: BMI = weight in kilograms divided by height in metres squared (kg/m²). A BMI under 18.5 is classed as underweight, 18.5–24.9 as normal, 25–29.9 as overweight, and 30 or above as obese. The calculator also shows the healthy weight range for your height, so you can see exactly how many kilograms or pounds separate you from the normal band.
BMI is used by doctors, dietitians and fitness coaches as a first-line screening tool, but it is not a diagnosis. It does not distinguish muscle from fat, so athletes may read high while carrying little fat. Use it as a starting point, and pair it with our calorie calculator to plan your daily energy intake.
How to Use the BMI Calculator
- 1Choose metric (cm, kg) or imperial (ft/in, lbs) units.
- 2Enter your height and weight.
- 3Read your BMI value and WHO category instantly.
- 4Check the healthy weight range shown for your height.
Frequently Asked Questions
How is BMI calculated?
BMI equals your weight in kilograms divided by the square of your height in metres (kg/m²). For imperial units the calculator converts feet, inches and pounds to metric first, so the result is identical. For example, 70 kg at 1.75 m gives a BMI of 22.9, which falls in the normal range.
What is a healthy BMI range?
According to the WHO, a BMI between 18.5 and 24.9 is considered the normal or healthy range for adults. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classed as obese. Some Asian populations use a lower overweight cut-off of 23 for health-risk screening.
Is BMI accurate for athletes and bodybuilders?
Not always. BMI cannot tell muscle from fat, so muscular people often register as overweight despite low body fat. Similarly, older adults with low muscle mass may show a normal BMI while carrying excess fat. For these cases, waist circumference or body-fat percentage measurements give a better picture.
Does BMI differ for men and women?
The WHO adult BMI categories are the same for men and women. However, women naturally carry more body fat than men at the same BMI, and health risk varies with age, ethnicity and fat distribution. Treat BMI as one indicator among several, not a complete health assessment.
Is this BMI calculator suitable for children?
No. For children and teens aged 2–19, BMI must be interpreted against age- and sex-specific percentile charts rather than fixed adult cut-offs. This tool uses the adult WHO classification, so consult a paediatric growth chart or your doctor for anyone under 20.