BMI calculator (body mass index)
Calculate your BMI and see the healthy weight range for your height.
Calculator inputs
Results
Enter your values and press “Calculate” to see the result.
In short
- What it calculates
- Calculate your BMI and see the healthy weight range for your height.
- Formula used
BMI = weight (kg) / height (m)²- Example
- Weight 70 kg and height 175 cm:
BMI calculator
Body mass index relates your weight to your height and is the reference the World Health Organization uses to classify body weight in adults.
Alongside the index you get the weight range considered healthy for your height.
How it works
Weight in kilograms is divided by the square of height in metres. If you type your height in centimetres, the calculator converts it automatically.
The healthy range comes from rearranging the formula for a BMI between 18.5 and 24.9.
Formula
BMI = weight (kg) / height (m)²
WHO classification:
< 18.5 underweight
18.5 – 24.9 normal weight
25 – 29.9 overweight
30 – 34.9 obesity class I
35 – 39.9 obesity class II
≥ 40 obesity class III
Worked example
Weight 70 kg and height 175 cm:
BMI = 70 / 1.75² = 70 / 3.0625 = 22.86
Normal weight. The healthy range for 1.75 m runs from 56.7 kg to 76.3 kg.
Explanation
It was created to study populations, not individuals
Adolphe Quetelet devised the index in the nineteenth century as a statistical tool for describing the average build of a population. He was not a physician and did not intend to diagnose anyone. Its individual clinical use came much later, and it carries the limitations of a formula never designed for it.
What the formula cannot see
It does not distinguish muscle from fat, nor does it know where that fat sits. An athlete with substantial lean mass lands in the overweight range. A sedentary person with little muscle can sit in the normal range with a high body fat percentage. The same figure describes opposite situations.
Where the fat is matters more than how much
Abdominal fat is associated with far higher cardiovascular and metabolic risk than peripheral fat. That is why waist circumference and the waist-to-height ratio predict risk better than body mass index. Keeping your waist below half your height is a simple and fairly robust rule.
Children and older people read differently
In childhood, age and sex percentiles are used rather than adult ranges. In older people, loss of muscle mass and height distorts the result, and healthy thresholds are usually set somewhat higher.
Frequently asked questions
Does BMI work for athletes?
Only with caution. Muscle weighs more than fat, so an athlete can exceed 25 without excess body fat. Measuring body fat percentage is more useful there.
What about children?
Not directly. For under-18s, percentiles by age and sex are used, because reference values shift during growth.
Which BMI is considered healthy?
Between 18.5 and 24.9 according to the WHO, though the optimal range may shift slightly with age.
Why does BMI fail for athletes?
Because it does not distinguish muscle from fat. A heavily muscled person weighs more for their height and lands in the overweight range without excess fat.
Which measurement best complements BMI?
Waist circumference and the waist-to-height ratio, because they show where fat accumulates, which matters most for cardiovascular risk.
Need to calculate something else?
These tools are often used alongside this calculator.
Ideal weight
Four classic formulas plus the healthy range from BMI.
Body fat
US Navy method estimate from your body circumferences.
BMR
The calories your body burns at complete rest, from two formulas.
Calories
The calories you need for your goal, with the protein, fat and carb split.
TDEE
Calories you burn each day given your metabolism and activity level.
Due date
Estimated birth date adjusted to your actual cycle length.