About the BMI Calculator
The BMI Calculator works out your body mass index from your height and weight, in feet, inches and pounds or in centimeters and kilograms. It shows the adult category used by the CDC and the World Health Organization, the weight range that counts as healthy for your height, and your BMI Prime.
BMI is a quick, widely used way to screen adults for weight that may affect health. Doctors use it as a starting point, because it needs nothing more than a tape measure and a scale. It does not measure body fat directly, though, and it works less well for some groups, such as athletes, older adults and children. The sections below explain those limits.
BMI is a screening estimate, not medical advice. It cannot diagnose a health condition. Talk to a doctor or another health professional about your weight and health. Everything is calculated in your browser, and nothing you enter is stored or sent.
How to use it
- Choose your unitsPick Imperial for feet, inches and pounds, or Metric for centimeters and kilograms. Your numbers are converted when you switch.
- Enter your height and weightType your height and your current weight. Decimals are fine, such as 5 feet 8.5 inches.
- Add your age if you likeAge is optional. Under 20, the tool reminds you that the adult categories do not apply.
- Read your BMI and categoryYour BMI is shown with one decimal, together with its category, a marker on the scale and the matching row in the table.
- Check the extra numbersSee the healthy weight range for your height, how far you are from it, and your BMI Prime.
Key features
Imperial and metric
Feet, inches and pounds or centimeters and kilograms, with exact conversion between them.
Standard adult categories
The cut-offs used by both the CDC and the WHO: underweight, healthy weight, overweight and three classes of obesity.
Healthy weight range
The weights that give a BMI from 18.5 to 24.9 at your height.
BMI Prime
Your BMI divided by 25, the upper limit of the healthy range. Below 1.00 is under that limit.
Age reminder for children and teens
Under 20, BMI needs age and sex-specific charts, and the tool says so.
Private by design
No account and no upload. Your height and weight stay in your browser.
Examples
How BMI is calculated
BMI is your weight divided by your height squared:
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²For 5 feet 9 inches (69 inches) and 159 pounds: 703 × 159 ÷ 69² = 703 × 159 ÷ 4,761 = 23.5. In metric, 175 cm and 72 kg give 72 ÷ 1.75² = 72 ÷ 3.0625 = 23.5 as well.
Adult categories (CDC and WHO)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Obesity class 1 |
| 35 to 39.9 | Obesity class 2 |
| 40 and above | Obesity class 3 (severe obesity) |
These cut-offs apply to adults aged 20 and older, men and women alike. The category follows the BMI as shown with one decimal, so 24.96 is shown as 25.0 and counts as overweight.
Some results
| Height and weight | BMI | Category | Healthy range |
|---|---|---|---|
| 5 ft 4 in, 140 lb | 24.0 | Healthy weight | 107.8 to 145.1 lb |
| 5 ft 10 in, 175 lb | 25.1 | Overweight | 128.9 to 173.5 lb |
| 6 ft 0 in, 200 lb | 27.1 | Overweight | 136.4 to 183.6 lb |
| 180 cm, 110 kg | 34.0 | Obesity class 1 | 59.9 to 80.7 kg |
For 5 feet 10 inches and 175 pounds, the tool shows "Lose 1.5 lb" to reach the healthy range and a BMI Prime of 1.00. A difference that small is well within normal day-to-day changes in body weight.
Where BMI falls short
- Athletes and muscular people: muscle weighs more than fat, so a strong, lean person can have a BMI in the overweight range without carrying extra fat.
- Older adults: people tend to lose muscle and height with age, so a "healthy" BMI can hide more body fat than it suggests. Doctors often look at weight changes, strength and waist size as well.
- Children and teens (2 to 19): the adult categories do not apply. Their BMI is compared with others of the same age and sex on growth charts. In the CDC charts, below the 5th percentile is underweight, the 5th to under the 85th is healthy weight, the 85th to under the 95th is overweight, and the 95th and above is obesity.
- Other groups: BMI is not used during pregnancy, and health risks can start at a lower BMI in some populations, such as people of Asian descent.
Tips
- Weigh yourself at the same time of day, ideally in the morning before eating, for numbers you can compare over time.
- Measure your height without shoes, standing straight against a wall. Being off by an inch changes the BMI by about 0.7 at average heights.
- Look at the trend, not one reading. A change of a few pounds from day to day is mostly water.
- Pair BMI with your waist size. Health agencies use a waist over 40 inches for men and 35 inches for women, about 102 and 88 cm, as an extra sign of risk.
- Bring your numbers to your next checkup. A doctor can put them in context with blood pressure, blood tests and your history.
Common mistakes and limits
- Reading BMI as a diagnosisBMI is a screening estimate. It does not show body fat, fitness or health on its own, and it is not medical advice.
- Using adult categories for children and teensUnder 20, BMI must be read on age and sex-specific percentile charts. The adult categories can be badly misleading for a growing child.
- Judging muscular people by BMI aloneAthletes and people who lift weights can be "overweight" by BMI with low body fat. Waist size or a body fat measurement tells more.
- Ignoring muscle loss in older adultsA normal BMI in later life can hide low muscle and higher body fat. Strength and unplanned weight loss matter as much as the number.
- Mixing up unitsEnter pounds with feet and inches, and kilograms with centimeters. The tool converts when you switch, but typing kilograms into the pounds box gives a wrong result.