BMI Calculator
Calculate your Body Mass Index (BMI) in metric or imperial units, find your category and ideal weight range.
BMI is a screening tool and doesn’t diagnose health. Talk to a healthcare provider for personal advice.
What is BMI?
Body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters. It’s a simple, inexpensive screening method for weight category: underweight, healthy weight, overweight, and obesity.
Why is BMI Important?
BMI correlates with amount of body fat, and higher BMI values are associated with increased risk for various health conditions including:
- Heart disease
- High blood pressure
- Type 2 diabetes
- Gallstones
- Breathing problems
- Certain cancers
BMI Limitations
While BMI is a useful screening tool, it has limitations:
- May overestimate body fat in athletes and those with muscular build
- May underestimate body fat in older persons and those who have lost muscle
- Does not directly measure body fat
- Does not account for factors like age, sex, ethnicity, and muscle mass
How to Calculate BMI
The BMI formula is simple:
BMI = weight(kg) / height(m)²
For those using imperial measurements, the formula is slightly different:
BMI = [weight(lb) / height(in)²] × 703
Understanding Your BMI Results
The World Health Organization defines adult BMI categories as:
| Category | BMI Range | Health Risk |
|---|---|---|
| Underweight | < 18.5 | Increased risk of health problems |
| Normal weight | 18.5 – 24.9 | Least risk of health problems |
| Overweight | 25.0 – 29.9 | Increased risk of health problems |
| Obesity Class I | 30.0 – 34.9 | High risk of health problems |
| Obesity Class II | 35.0 – 39.9 | Very high risk of health problems |
| Obesity Class III | ≥ 40.0 | Extremely high risk of health problems |
Maintaining a Healthy Weight
If your BMI indicates you’re outside the healthy range, consider these steps:
- Consult with a healthcare provider for personalized advice
- Adopt a balanced diet with appropriate portions
- Engage in regular physical activity (150 minutes moderate exercise per week)
- Get adequate sleep (7-9 hours per night for adults)
- Manage stress through techniques like meditation or yoga
Frequently Asked Questions
Is BMI accurate for everyone?
BMI provides a general indicator of body fatness for most people but may be less accurate for athletes (who have high muscle mass), the elderly, and certain ethnic groups.
Should children use the same BMI calculator?
No, children and teens require age and sex-specific percentile calculations because their body composition varies as they age. This calculator is designed for adults aged 20+.
What’s a healthy BMI for older adults?
Some research suggests that a slightly higher BMI (between 25-27) may be protective for older adults, as being slightly overweight may provide energy reserves during illness.
How often should I check my BMI?
For most adults, checking every few months is sufficient unless you’re actively trying to change your weight. Dramatic changes in BMI warrant a discussion with your healthcare provider.