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BMI Calculator

Work out your Body Mass Index and the healthy weight range for your height, in metric or imperial units.

Runs locally — files never leave your device

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How to use BMI Calculator

  1. 1Choose Metric (cm and kg) or Imperial (feet, inches and pounds).
  2. 2Enter your height and weight. The BMI updates as you type.
  3. 3Read your BMI, its WHO category and where it sits on the scale.
  4. 4Check the healthy weight range for your height shown below the scale.

Calculate your Body Mass Index

Body Mass Index (BMI) is a simple number that relates your weight to your height. Doctors and health organisations use it as a first screening tool for weight categories that may affect health. This BMI calculator works in metric or imperial units, shows your category on a colour-coded scale, and tells you the weight range that corresponds to a healthy BMI for your height. Your measurements never leave your browser.

BMI categories for adults

BMI WHO category
Below 18.5 Underweight
18.5 – 24.9 Normal weight
25.0 – 29.9 Overweight
30.0 – 34.9 Obesity class I
35.0 – 39.9 Obesity class II
40 and above Obesity class III

These ranges apply to adults of all ages and both sexes. For some Asian populations, guidelines in several countries set lower cut-offs (for example, overweight from 23 and obesity from 25 or 27.5) because health risks rise at lower BMI levels.

How to use your result

Within the normal range? BMI suggests your weight is in a range associated with the lowest risk for most people. Staying active and eating well matter regardless of the number.

Below 18.5? Being underweight can be linked to nutritional deficiencies, weakened immunity and bone loss. If you have lost weight without trying, talk to a doctor.

25 or above? Higher BMI is associated with increased risk of type 2 diabetes, high blood pressure and heart disease. Waist size is a useful second check: a waist above about 94 cm (37 in) for men or 80 cm (31.5 in) for women indicates increased risk in many guidelines.

Limitations of BMI

BMI was designed for populations, not individuals. It overestimates body fat in muscular people and can underestimate it in older adults who have lost muscle. It is not suitable for children, pregnant women or competitive athletes. Use it as a starting point for a conversation with a health professional, not as a diagnosis.

Need to convert your height or weight between units first? Use the Unit Converter.

Frequently asked questions

How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres (kg/m²). For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9. With imperial units the tool converts pounds and inches to metric first, so results are identical.
What is a healthy BMI?
For adults, the World Health Organization classifies BMI as: under 18.5 underweight, 18.5–24.9 normal (healthy) weight, 25–29.9 overweight, and 30 or more obese. Some health authorities use lower thresholds for people of Asian descent, for example 23 for overweight.
Is BMI accurate for everyone?
No. BMI is a quick screening measure based only on height and weight. It does not distinguish muscle from fat, so athletes may score as "overweight" while being healthy, and it does not show where fat is stored. Waist circumference, body composition and a doctor's assessment give a fuller picture.
Can children use this BMI calculator?
Not reliably. For children and teenagers, BMI must be compared with age- and sex-specific growth charts (percentiles). This calculator uses adult categories, which apply from age 18 (or 20 in some guidelines).
Does BMI apply during pregnancy?
No. Weight gain during pregnancy is expected, so BMI categories do not apply. Healthcare providers use pre-pregnancy BMI to recommend a healthy amount of weight gain.
Is my data saved?
No. Your height and weight are processed only in your browser and are not stored or sent anywhere.

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