BMI Calculator
Free BMI calculator. Enter your weight and height in metric or imperial to get your body mass index and WHO weight category instantly.
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Body Mass Index
Underweight
Normal
Overweight
Obesity
| Body Mass Index (BMI) | 24.2 kg/m2 |
|---|---|
| BMI Category | Healthy weight |
| Healthy BMI range | 18.5 kg/m2 - 25 kg/m2 |
| Healthy weight for the height | 135.1 lbs - 182.6 lbs |
| Gain to reach a BMI of 18.5 kg/m2 | - |
| Lose to reach a BMI of 25 kg/m2 | - |
| Ponderal Index | 13.27 kg/m3 |
BMI calculator at a glance#
A BMI calculator works out your body mass index from your weight and height. In metric, BMI is your weight in kilograms divided by your height in metres squared. In imperial, it is 703 times your weight in pounds divided by your height in inches squared. The result places you in a weight category.
Worked example: at 70 kg and 1.75 m, 1.75 squared is 3.0625, so 70 divided by 3.0625 is a BMI of 22.9, which is in the normal range. The same person at 154 lb and 68 in gives 703 times 154 divided by 4,624, which is 23.4, again normal.
| Bmi | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Normal weight |
| 25.0–29.9 | Overweight |
| 30.0 and above | Obese |
Enter your weight and height in the calculator above for your exact BMI and category. These bands come from the WHO and apply to adults aged 20 and over. BMI does not separate fat from muscle, so very muscular people can read high, and the cut-offs differ for children and teens, who are scored by age and sex percentile.
How to read your BMI result#
Your BMI maps to one of four adult categories: underweight, normal, overweight or obese. The answer block above lists the exact cut-offs. The number is a screening tool, not a diagnosis. It sorts a population by weight for height, but it cannot see if your weight is fat or muscle, so read it alongside your waist size, activity level and how you feel rather than on its own.
BMI for children and teens#
The adult bands do not apply to anyone under 20. For ages 2 to 19, BMI is plotted against CDC growth charts and scored as a percentile for the child's age and sex, because healthy body fat changes as kids grow. The CDC categories are: underweight below the 5th percentile, healthy weight from the 5th to under the 85th, overweight from the 85th to under the 95th, and obese at or above the 95th. Use a pediatric BMI percentile chart for these ages, not the adult table.
Where BMI falls short#
BMI does not separate fat from muscle, so it can mislabel some people. A muscular athlete can read overweight or obese while carrying little fat, and an older adult who has lost muscle can read normal while carrying excess fat. It also does not account for where fat sits; abdominal fat carries more health risk than fat on the hips. Fat distribution, age, sex and ethnicity all shift what a given BMI means, which is why a body fat percentage estimate or a waist measurement can add useful context.
An estimate, not a diagnosis#
Treat BMI as a starting point. A reading outside the normal range is a reason to look closer, not a verdict on your health. Your weight is one of several signals, and a clinician can weigh it against your medical history, body composition and lifestyle.
Frequently asked questions#
How do I use a BMI calculator?#
Enter your weight in pounds or kilograms and your height in feet and inches or in centimeters. The calculator returns your BMI and the matching category. The metric and imperial formulas are in the answer block above.
What does BMI measure?#
It measures weight relative to height as a single number, used to screen for underweight, overweight and obesity. It estimates body fatness indirectly but does not measure fat directly.
What is a healthy BMI range?#
For adults, 18.5 to 24.9 is the normal range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 and above is obese.
Is BMI the same for children and adults?#
No. Children and teens aged 2 to 19 are scored by percentile against CDC growth charts for their age and sex. Only adults use the fixed 18.5 to 24.9 normal band.
Can muscle mass affect BMI?#
Yes. Because BMI counts all weight the same, very muscular people can read high without excess fat. In those cases a body fat percentage estimate is more informative.
Is BMI different in metric and imperial units?#
The result is the same; only the formula changes. Metric is weight in kg divided by height in metres squared. Imperial is 703 times weight in pounds divided by height in inches squared.
Can two people with the same BMI have different bodies?#
Yes. BMI does not distinguish fat from muscle, so two people at the same height and BMI can have very different body compositions.
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