BMI Calculator
Calculate your Body Mass Index and find out your weight category.
Your BMI
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About BMI Calculator
Body Mass Index (BMI) is a simple calculation used to assess whether a person has a healthy body weight for their height. It was developed in the 19th century by Belgian mathematician Adolphe Quetelet and remains one of the most widely used screening tools for weight categories.
How is BMI Calculated?
The BMI formula is straightforward:
BMI = weight (kg) ÷ height² (m²)
For imperial units, the formula is adjusted: BMI = (weight in lbs × 703) ÷ height² (inches²)
BMI Categories (WHO Standards)
| Category | BMI Range |
|---|---|
| Severe Underweight | < 16 |
| Underweight | 16 - 18.5 |
| Normal (Healthy) | 18.5 - 24.9 |
| Overweight | 25 - 29.9 |
| Obese Class I | 30 - 34.9 |
| Obese Class II | 35 - 39.9 |
| Obese Class III | ≥ 40 |
Limitations of BMI
While BMI is a useful screening tool, it has limitations:
- Muscle Mass: Athletes and bodybuilders may have a high BMI despite being healthy due to muscle weight.
- Age: Older adults may have more body fat than younger adults with the same BMI.
- Ethnicity: BMI thresholds may differ for different ethnic groups.
- Body Composition: BMI doesn't distinguish between fat, muscle, and bone mass.
Frequently Asked Questions
What is a healthy BMI?
A healthy BMI falls between 18.5 and 24.9. This range is associated with the lowest health risks for most adults. However, individual factors like muscle mass, age, and ethnicity should also be considered.
Is BMI accurate for athletes?
BMI may not be accurate for athletes or muscular individuals because muscle weighs more than fat. A bodybuilder with low body fat might still have a "overweight" BMI. In such cases, body fat percentage is a better indicator.
Does BMI apply to children?
For children and teens (ages 2-19), BMI is calculated the same way but interpreted using age- and sex-specific percentiles. This is because body composition varies with age and between boys and girls.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of normal). A BMI Prime of 1.0 means you're at the upper limit of normal weight. Values below 1.0 indicate underweight to normal, while values above 1.0 indicate overweight.
How often should I check my BMI?
If you're actively managing your weight, checking monthly can help track progress. Otherwise, checking every few months or during annual health checkups is sufficient.
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