BMI Calculator - Body Mass Index
Calculate your Body Mass Index (BMI) to determine if you're at a healthy weight for your height. BMI is a useful screening tool, but it does have limitations.
How do I calculate BMI?
The Body Mass Index (BMI) is calculated using a simple formula that divides your weight by the square of your height:
BMI = weight (kg) ÷ height² (m²)
For example, if you weigh 70 kg and are 1.75 meters tall:
- BMI = 70 ÷ (1.75 × 1.75)
- BMI = 70 ÷ 3.0625
- BMI = 22.9
If you prefer to use pounds and inches:
BMI = [weight (lb) ÷ height² (in²)] × 703
Normal BMI
According to the World Health Organization (WHO), BMI values are classified as follows:
| BMI Range | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal 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 |
A BMI between 18.5 and 24.9 is considered normal or healthy weight for most adults. However, these ranges may not be appropriate for all ethnic groups, athletes, children, or the elderly.
What are the BMI ranges?
BMI ranges are categorized to help identify potential health risks associated with being underweight, overweight, or obese:
- Underweight (BMI below 18.5): May indicate malnutrition, an eating disorder, or other health problems.
- Normal weight (BMI 18.5-24.9): Generally associated with the lowest health risks for most adults.
- Overweight (BMI 25.0-29.9): May increase the risk of heart disease, high blood pressure, type 2 diabetes, and other health problems.
- Obesity class I (BMI 30.0-34.9): Associated with higher risks of health problems.
- Obesity class II (BMI 35.0-39.9): Associated with even higher health risks.
- Obesity class III (BMI 40.0 and above): Also known as severe or morbid obesity, associated with the highest risk of health problems.
BMI Prime is another way to interpret BMI. It's the ratio of your BMI to the upper limit of the normal BMI range (25). A BMI Prime less than 0.74 is underweight, 0.74-0.99 is normal weight, and 1.0 or greater is overweight.
Using our body mass index calculator
Our BMI calculator is easy to use and provides instant results:
- Select your sex (male or female)
- Enter your height (in centimeters, feet and inches, or just inches)
- Enter your weight (in kilograms or pounds)
- The calculator will automatically display your BMI, BMI category, and BMI Prime
You can also click on "BMI percentile and athletes" to see additional information about BMI percentiles and considerations for athletes.
Other considerations
While BMI is a useful screening tool, it has several limitations:
- Muscle mass: BMI doesn't distinguish between fat and muscle. Athletes and people with high muscle mass may have a high BMI despite having low body fat.
- Body fat distribution: BMI doesn't account for where fat is stored. Abdominal fat (around the waist) poses greater health risks than fat stored in the hips and thighs.
- Age: BMI may not be as accurate for elderly people, who tend to lose muscle mass as they age.
- Ethnicity: Different ethnic groups may have different body compositions and health risks at the same BMI.
- Pregnancy: BMI is not applicable during pregnancy.
For a more comprehensive assessment of your health, consider combining BMI with other measurements such as waist circumference, body fat percentage, and consultation with healthcare professionals.
FAQs
Is BMI accurate for everyone?
No, BMI has limitations. It may not be accurate for athletes, elderly people, pregnant women, or certain ethnic groups. It doesn't distinguish between fat and muscle mass.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, what's healthy can vary based on factors like age, ethnicity, and body composition.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of the normal BMI range). A BMI Prime of 1.0 means your BMI is exactly at the upper limit of the normal range. Values below 1.0 indicate normal or underweight, while values above 1.0 indicate overweight or obesity.
How often should I check my BMI?
For most adults, checking BMI once or twice a year is sufficient. If you're actively trying to lose or gain weight, you might want to check more frequently, but focus more on other measures of progress like how your clothes fit, energy levels, and overall health.