BMI Calculator - Check Your Body Mass Index
Our BMI Calculator helps you calculate your Body Mass Index (BMI) quickly and accurately, taking your age into consideration. Use the "Metric Units" tab for kilograms and meters, or the "Other Units" tab to convert to US units like pounds and inches. In addition to BMI, this tool also calculates the Ponderal Index (PI), which can be useful for very tall or short individuals.
What is BMI (Body Mass Index)?
BMI is a measure of your leanness or corpulence based on your height and weight. It is widely used to assess whether your weight is healthy for your height. The resulting number helps classify your weight status into underweight, normal weight, overweight, or obese categories. These ranges can vary depending on region, age, and sometimes gender, and they may include further subcategories like severely underweight or very severely obese.
BMI Table for Adults (20+ years)
Based on World Health Organization (WHO) recommendations:
| Classification | BMI (kg/m²) |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16 - 17 |
| Mild Thinness | 17 - 18.5 |
| Normal | 18.5 - 25 |
| Overweight | 25 - 30 |
| Obese Class I | 30 - 35 |
| Obese Class II | 35 - 40 |
| Obese Class III | > 40 |
BMI Table for Children and Teens (2-20 years)
According to CDC guidelines, BMI is interpreted using age- and gender-specific percentiles:
| Category | Percentile Range |
|---|---|
| Underweight | <5% |
| Healthy weight | 5% - 85% |
| At risk of overweight | 85% - 95% |
| Overweight | >95% |
Health Risks of Being Overweight
Being overweight increases the risk of serious health issues, including:
- High blood pressure and cholesterol imbalance
- Type 2 diabetes
- Heart disease, stroke, and gallbladder problems
- Osteoarthritis and joint issues
- Sleep apnea and breathing problems
- Certain cancers (breast, colon, kidney, liver)
- Mental health challenges and lower quality of life
- Increased risk of mortality
Health Risks of Being Underweight
Being underweight also comes with its own health risks:
- Malnutrition, vitamin deficiencies, anemia
- Osteoporosis and weak bones
- Lowered immunity
- Growth and developmental issues in children
- Potential reproductive issues for women
- Complications during surgery
- Increased risk of mortality
Limitations of BMI
While BMI is a useful tool, it has some limitations:
- It doesn’t differentiate between fat and muscle mass.
- Older adults usually have more body fat than younger adults at the same BMI.
- Women naturally have more body fat than men for the same BMI.
- Athletes and muscular individuals may have high BMI but low body fat.
- In children, height and puberty stage can influence BMI interpretation.
Overall, BMI is indicative of body fat for 90–95% of the population, but it should be combined with other measurements for a complete health assessment.
BMI Formula
To calculate BMI:
- US Units: BMI = 703 × mass (lbs) / height² (in)
Example: 5'10" (70 in), 160 lbs → BMI = 23.0 - SI, Metric Units: BMI = mass (kg) / height² (m)
Example: 72.57 kg, 1.778 m → BMI = 23.0
BMI Prime
BMI Prime compares a person’s BMI to the upper limit of normal (25 kg/m²). It helps quickly assess whether someone is underweight, normal, overweight, or obese.
| Classification | BMI | BMI Prime |
|---|---|---|
| Severe Thinness | <16 | <0.64 |
| Moderate Thinness | 16-17 | 0.64-0.68 |
| Mild Thinness | 17-18.5 | 0.68-0.74 |
| Normal | 18.5-25 | 0.74-1 |
| Overweight | 25-30 | 1-1.2 |
| Obese Class I | 30-35 | 1.2-1.4 |
| Obese Class II | 35-40 | 1.4-1.6 |
| Obese Class III | >40 | >1.6 |
Ponderal Index (PI)
The Ponderal Index (PI) is similar to BMI but uses height cubed instead of squared. It is more reliable for very tall or short individuals.
- US Units: PI = height (in) / ∛mass (lbs)
Example: 70 in, 160 lbs → PI = 12.9 - SI Units: PI = mass (kg) / height³ (m)
Example: 72.57 kg, 1.778 m → PI = 12.9