BMI Calculator
Body mass index from height and weight in metric or US units, with the WHO adult category and its limits explained.
Your measurements
Filled in with example values. Replace them with your own.
Results update as you type.
Result
BMI 24.7 (Healthy weight)
Your BMI
24.7Healthy weight
An estimate, not medical advice. This result is based on a general formula and cannot diagnose anything or account for your health. For advice about your weight, diet or health, talk to a doctor or a registered dietitian.
- BMI, unrounded
- 24.69
- BMI 18.5–24.9 at your heightThe weight range WHO calls healthy for adults
- 59.9 kg – 80.7 kg
Adult BMI categories (WHO)
- UnderweightBelow 18.5
- Healthy weight18.5 – 24.9
- Overweight25 – 29.9
- Obesity class I30 – 34.9
- Obesity class II35 – 39.9
- Obesity class III40 or more
How it’s calculated
Height squared
1.8 m × 1.8 m = 3.24 m²
BMI
80 kg ÷ 3.24 m² = 24.7
Important
This calculator gives a general estimate from a published formula. It is not a diagnosis and not medical advice, and it cannot take your health, medicines or history into account. BMI is a screening measure for groups of people and cannot tell how healthy one person is.For advice about your weight, diet or health, talk to a doctor or a registered dietitian. See theDisclaimer.
How the BMI calculator works
Body mass index (BMI) is your weight in kilograms divided by the square of your height in metres. Enter your height and weight in metric or US units; US units are converted to metric first.
For adults, the result is placed in one of the categories used by the World Health Organization. For people under 20, no adult category is shown, because their BMI is read against growth charts for their age and sex.
The formula
BMI = Weight (kg) ÷ Height (m)²
Adult BMI categories (WHO)
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25.0 to 29.9: overweight
- 30.0 to 34.9: obesity class I
- 35.0 to 39.9: obesity class II
- 40.0 or more: obesity class III
Worked examples
- 180 cm and 80 kg: 1.8 × 1.8 = 3.24 m², and 80 ÷ 3.24 = 24.7, in the healthy weight range. At this height, BMI 18.5 to 24.9 corresponds to about 59.9 to 80.7 kg.
- 5 ft 9 in and 160 lb: 69 in = 175.26 cm and 160 lb = 72.57 kg, so BMI = 72.57 ÷ 1.7526² = 23.6.
Limitations
- BMI does not tell muscle from fat, or show where fat is carried on the body.
- The adult categories do not apply to children, teenagers or during pregnancy.
- The same BMI can carry different health risks for people of different ages, sexes and ethnic backgrounds.
- Heights from 100 to 250 cm and weights from 20 to 350 kg are accepted; values outside are most likely typos.
Frequently asked questions
Does BMI measure body fat?
No. BMI only compares weight with height. Two people with the same BMI can have very different amounts of muscle and fat, so a muscular person can have a high BMI without excess fat, and someone with little muscle can have a “healthy” BMI with a high share of fat.
Why is there no category for under-20s?
Children and teenagers are still growing, and their healthy BMI changes with age and differs between boys and girls. Their BMI is read as a percentile on a growth chart, which a doctor or school nurse can do. Enter an age under 20 and the calculator shows the BMI without an adult category.
Are the ranges the same for everyone?
The categories here are the World Health Organization ranges for adults. Some health bodies use lower thresholds for people from certain ethnic backgrounds, for example NICE in the UK, because health risks can rise at a lower BMI. BMI is also not used to judge weight during pregnancy.
Why does my BMI differ slightly from another calculator?
This calculator converts inches and pounds exactly (1 in = 2.54 cm, 1 lb = 0.45359237 kg). The common shortcut of weight in pounds × 703 ÷ height in inches² gives a very slightly different number. The category is based on the BMI rounded to one decimal, the value you see.
What should I do with the result?
Use it as one rough indicator. If you are concerned about your weight or health, a doctor can look at it together with other measures, such as waist size, blood pressure and your medical history.