BMI Calculator
Body mass index with your category and healthy weight range.
Body Mass Index
- Category
- Normal
- Healthy weight range
- 59.9 kg – 80.7 kg
BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat or account for age, sex, or build. Discuss your results with a clinician.
How the BMI calculator works
Body Mass Index is a single number that relates your weight to your height. The formula is your weight in kilograms divided by the square of your height in metres:
BMI = weight(kg) / height(m)^2
The calculator accepts either metric (kilograms and centimetres) or imperial (pounds and inches) input. Imperial values are converted first, using the exact factors 1 lb = 0.45359237 kg and 1 in = 2.54 cm, so both unit systems produce the same result. Height in centimetres is divided by 100 to get metres before squaring.
The result is sorted into the CDC adult categories:
- Underweight below 18.5
- Normal 18.5 to 24.9
- Overweight 25 to 29.9
- Obese 30 and above
The boundaries are inclusive at the bottom of each higher band, so a BMI of exactly 25.0 reads as overweight, not normal. The tool also reports a healthy weight range for your height by inverting the normal band: the lowest healthy weight is 18.5 * height(m)^2 and the highest is 24.9 * height(m)^2.
Worked example
Take someone who is 180 cm tall and weighs 80 kg.
- Height in metres:
180 / 100 = 1.8 - Height squared:
1.8 * 1.8 = 3.24 - BMI:
80 / 3.24 = 24.69
That sits inside the normal band, so the category is Normal. The healthy weight range for 1.8 m is 18.5 * 3.24 = 59.94 kg at the low end and 24.9 * 3.24 = 80.68 kg at the high end, which means 80 kg is near the top of healthy.
If the same person weighed 100 kg instead, the BMI would be 100 / 3.24 = 30.86, which lands in the Obese band.
The same answers come out in imperial. Someone 71 in tall weighing 154 lb converts to about 180.34 cm and 69.85 kg, giving a BMI of 21.48, comfortably Normal.
How to use it
- Pick your unit system, then enter your weight and height.
- Read your BMI, its category, and the healthy weight range for your height.
- Switch units at any time. The calculator reconverts your figures, so you do not need to do the arithmetic yourself.
Limitations
BMI is a screening measure, not a diagnosis or direct measurement of body fat. It uses only height and weight, so it cannot distinguish muscle from fat, show fat distribution, or incorporate medical history, laboratory findings, fitness, or other clinical factors. These categories are for adults age 20 and older and should not be applied to children or teens. Discuss concerning results with a healthcare professional who can interpret them in context.
Sources and scope
- Jurisdiction
- Adult screening categories; CDC guidance for adults age 20 and older
- Data current to
- July 30, 2026
- Last updated
- Adult BMI Calculator — Centers for Disease Control and Prevention
- BMI Frequently Asked Questions — Centers for Disease Control and Prevention
Frequently asked questions
What is a healthy BMI?
For adults, the World Health Organization treats a BMI from 18.5 up to but not including 25 as the healthy range. Below 18.5 is underweight, 25 to just under 30 is overweight, and 30 or above is obese. These cut points are the same for men and women. They are population guides, not a personal diagnosis, so treat the band as a starting point rather than a target you must hit exactly.
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres. If you enter pounds and inches, the calculator first converts them to kilograms and centimetres using the exact factors 1 lb = 0.45359237 kg and 1 in = 2.54 cm, then applies the same formula. Working in one consistent unit system is what makes the number comparable across people.
Why does the same BMI mean different things for different people?
BMI only uses height and weight. It cannot tell muscle from fat, so a very muscular person can read as overweight while carrying little fat. It also does not account for age, sex, frame size, or where fat is stored. Two people with the same BMI can have very different health profiles, which is why it is a screening signal, not a verdict.
Is BMI accurate for children or athletes?
The categories in this tool are intended for adults age 20 and older. CDC interprets BMI for people ages 2 through 19 using age- and sex-specific percentiles. BMI can also misrepresent body composition in highly muscular people and is not an appropriate standalone assessment during pregnancy.
What can I use alongside BMI?
Waist circumference and waist to height ratio capture where fat sits, which matters more for cardiovascular and metabolic risk than total weight alone. Body fat percentage, blood pressure, blood glucose, and lipid panels give a fuller picture. BMI is best read as one quick input into that wider assessment.