Calculate your Body Mass Index (BMI) with WHO classifications — see your BMI Prime, Ponderal Index, healthy weight range, and CDC percentile charts for children and adults.
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The Body Mass Index (BMI) Calculator helps you determine your BMI value and corresponding weight status while considering your age. You can switch between US and Metric measurement systems using the tabs above. This comprehensive tool goes beyond simple BMI calculations by also computing the Ponderal Index and BMI Prime, giving you a more complete picture of your body composition and health status.
Whether you're tracking your fitness journey, monitoring your child's growth, or simply curious about your health metrics, this calculator provides valuable insights into body weight status based on standards from the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC).
BMI is a measurement that helps assess a person's body composition based on their height and weight. It's designed to estimate tissue mass and is widely used as a general indicator of whether someone has a healthy body weight for their height. The value you get from a BMI calculation places you in one of several categories: underweight, normal weight, overweight, or obese.
These BMI ranges can vary based on factors such as geographic region and age. Some classification systems further divide these categories into subcategories like severely underweight or very severely obese. While BMI isn't a perfect measure of healthy body weight, it serves as an excellent screening tool that helps identify whether additional testing or lifestyle changes might be needed.
Being either overweight or underweight can have significant health effects, which is why understanding your BMI can be an important first step in taking control of your health.
This table shows the World Health Organization's recommended body weight classifications based on BMI values for adults. These categories apply to both men and women, age 20 or older.
| Classification | BMI Range (kg/m²) | Health Risk |
|---|---|---|
| Severe Thinness | < 16 | High |
| Moderate Thinness | 16 - 17 | Moderate |
| Mild Thinness | 17 - 18.5 | Low |
| Normal | 18.5 - 25 | Healthy |
| Overweight | 25 - 30 | Increased |
| Obese Class I | 30 - 35 | High |
| Obese Class II | 35 - 40 | Very High |
| Obese Class III | > 40 | Extreme |
The Centers for Disease Control and Prevention (CDC) uses BMI percentiles to categorize weight status for children and teens between ages 2 and 20. Unlike adults, children's BMI is interpreted differently based on age and sex.
| Weight Category | Percentile Range | What This Means |
|---|---|---|
| Underweight | Less than 5th percentile | Child weighs less than 95% of peers of same age/sex |
| Healthy Weight | 5th to 85th percentile | Falls within the healthy weight range |
| Overweight | 85th to 95th percentile | Weighs more than 85% of peers |
| Obese | 95th percentile or above | Weighs more than 95% of peers of same age/sex |
Carrying excess weight increases the risk for several serious health conditions. According to the Centers for Disease Control and Prevention (CDC), the following conditions are associated with being overweight or obese:
Extra weight forces your heart to work harder, straining your cardiovascular system
Higher LDL (bad) cholesterol, lower HDL (good) cholesterol, and elevated triglycerides
Strong correlation between increased body weight and insulin resistance
Coronary heart disease from reduced blood flow to the heart muscle
Interruption of blood supply to brain tissue
Including gallstones and related complications
Joint disease caused by breakdown of cartilage from excess weight
Interrupted breathing during sleep, affecting rest and recovery
Endometrial, breast, colon, kidney, gallbladder, and liver cancer
Depression, anxiety, and reduced quality of life
Maintaining a BMI below 25 kg/m² can significantly reduce these risks. However, you should always consult your doctor to determine the best approach for your individual health needs.
Being underweight carries its own set of health risks that shouldn't be overlooked:
Vitamin deficiencies and anemia from inadequate nutrient absorption
Bone weakness increasing the risk of fractures
Decreased immune function making you more susceptible to infections
Developmental concerns, particularly in children and teenagers
Hormonal imbalances affecting menstrual cycles and fertility
Potential complications during and after surgical procedures
If you're concerned about being underweight, especially if the cause isn't obvious, consult your doctor. Conditions like anorexia nervosa require professional medical attention.
While BMI is a valuable screening tool, it's important to understand its limitations. BMI cannot distinguish between muscle and fat, so it should be used alongside other health measurements.
Athletes and bodybuilders may have high BMIs from muscle mass rather than fat. Older adults tend to have more body fat than younger adults with the same BMI. Women generally have more body fat than men at the same BMI.
Growth patterns vary. BMI is better at identifying obesity in children than identifying those who are simply overweight. Height and puberty stage influence BMI readings.
Bottom line: BMI accurately reflects body fat for about 90-95% of the population. Use it as a helpful starting point in your health journey, but not as the only measure of your wellbeing.
BMI = 703 × mass (lbs) / height² (in)
Example: 5'10", 160 lbs
= 703 × 160 / 70²
= 23.0
BMI = mass (kg) / height² (m)
Example: 178 cm, 72.57 kg
= 72.57 / 1.78²
= 23.0
BMI Prime is a simple ratio that compares your BMI to the upper limit of what's considered normal (25 kg/m²). It's a quick way to see how far you are from the healthy range.
| Category | 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 | 0.74-1.0 |
| Overweight | 25-30 | 1.0-1.2 |
| Obese Class I | 30-35 | 1.2-1.4 |
| Obese Class II | 35-40 | 1.4-1.6 |
| Obese Class III | > 40 | > 1.6 |
The Ponderal Index is similar to BMI but cubes the height instead of squaring it. This makes it more accurate for very tall or very short individuals, where BMI can sometimes over- or underestimate body fat.
For most adults, a healthy BMI ranges from 18.5 to 25 kg/m². However, this may vary based on age, ethnicity, and muscle mass. Always consult your healthcare provider for personalized guidance.
BMI is fairly accurate for about 90-95% of the population as a general health screening tool. However, it doesn't account for muscle mass versus fat mass, so very muscular individuals may have a high BMI without excess body fat.
BMI Prime is the ratio of your BMI to 25 (the upper limit of normal BMI). A value below 1 suggests normal weight, while values above 1 indicate overweight or obesity. It's a quick way to see how your BMI compares to the healthy threshold.
The Ponderal Index (PI) is similar to BMI but uses height cubed instead of squared. This makes it more reliable for very tall or very short individuals, where BMI can sometimes produce misleading results.
Children's BMI is calculated the same way as adults, but the results are interpreted differently using age- and sex-specific percentile charts. A child's BMI is compared to other children of the same age and sex.