How to use the BMI calculator
- Choose US units (feet, inches, pounds) or metric units (centimeters, kilograms).
- Enter your height and weight.
- Your BMI, weight category and healthy weight range appear instantly.
BMI formula
Body mass index compares your weight to your height:
Example: a person who is 175 cm tall and weighs 70 kg has a BMI of 70 ÷ 1.75² = 22.9. In US units, someone who is 5 ft 9 in (69 inches) and weighs 154 lb has a BMI of 703 × 154 ÷ 69² ≈ 22.7. Both fall in the normal weight range.
BMI chart for adults
The World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) use the following categories for adults:
| BMI | Weight status |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal (healthy) weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity, Class I |
| 35.0 – 39.9 | Obesity, Class II |
| 40.0 and above | Obesity, Class III (severe) |
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the normal range. A value below 1.0 means you are under the overweight threshold; 1.2 means your BMI is 20% above it. It makes it easy to see how far you are from the healthy range at a glance.
Limitations of BMI
BMI is a quick, inexpensive screening tool, but it does not measure body fat directly. Keep these limits in mind:
- Muscle mass: athletes and very muscular people may have a high BMI without excess fat.
- Age: older adults tend to have more body fat than younger adults at the same BMI.
- Body shape: BMI doesn't show where fat is stored. Abdominal fat carries more health risk, so waist size is a useful second measure.
- Ethnicity: health risks can begin at lower BMIs in some populations, including people of Asian descent.
- Pregnancy: BMI is not meaningful during pregnancy.
For a fuller picture, pair BMI with a body fat estimate and talk to your doctor about other health markers such as blood pressure and cholesterol.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy (normal) weight. A BMI of 25 to 29.9 is overweight, and 30 or higher is classified as obesity.
How do I calculate my BMI?
Divide your weight in kilograms by your height in meters squared. In US units, multiply your weight in pounds by 703 and divide by your height in inches squared.
Is BMI accurate?
BMI is a useful screening tool for populations, but it does not distinguish muscle from fat or show where fat is stored. Muscular people may be classified as overweight even if they have little body fat.
Is BMI different for men and women?
The adult BMI formula and categories are the same for men and women. However, women typically have more body fat than men at the same BMI.
Can children use this BMI calculator?
The categories shown here are for adults 20 and older. Children and teens are assessed using BMI-for-age percentiles, which account for growth and differences between boys and girls.
This calculator provides general information only and is not a substitute for professional medical advice, diagnosis or treatment. Always consult a doctor or other qualified health provider about your individual situation.
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