BMI Calculator
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Your BMI is
Underweight: < 18.5
Healthy Weight: 18.5 – 24.9
Overweight: 25.0 – 29.9
Obesity: ≥ 30.0
Note: BMI is a useful measure for most adults, but may not be accurate for athletes, pregnant women, or the elderly. Consult a healthcare provider for personalized advice.
Use our simple BMI calculator to help meet your weight management goals — just enter your height and weight, and get results in seconds!
BMI Directory – Find your BMI from a list of Heights.
What is BMI?
BMI (Body Mass Index) is a simple numerical measurement used to assess whether someone has a healthy body weight relative to their height.
BMI serves as a quick screening tool that healthcare providers, researchers, and public health officials use to identify potential weight-related health risks at a population level. It’s particularly useful because it requires only basic measurements and can be calculated easily.
How is BMI Calculated?
The formula for calculating BMI is straightforward. It’s calculated by dividing a person’s weight in kilograms by their height in meters squared (kg/m²), or weight in pounds divided by height in inches squared, then multiplied by 703.
Metric units:
Imperial units:
Limitations of BMI
While BMI is a useful screening tool, it has significant limitations. It doesn’t distinguish between muscle mass and fat mass, so very muscular individuals might be classified as overweight or obese despite having low body fat. It also doesn’t account for fat distribution, bone density, age, sex, or ethnicity – all factors that can affect the relationship between weight and health risk.
Additionally, BMI may not be as accurate for certain populations, including older adults, athletes, pregnant women, and some ethnic groups who may have different body compositions or health risk profiles at the same BMI levels.
While BMI remains a widely used tool, many healthcare providers now consider it alongside other measurements like waist circumference, body fat percentage, and overall health markers to get a more complete picture of someone’s health status.
BMI Table for Adults
| Classification | BMI range – 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 |
Adult BMI Chart
The following is an image of a BMI chart for adults from Wikipedia.
“Body Mass Index (BMI) Chart for Adults” by Cbizzy2313, [Link: Wikimedia Commons https://zh.wikipedia.org/wiki/commons:] (License: CC BY-SA).
BMI Table for Children and Teens aged 2 – 20
| Category | Percentile Range |
|---|---|
| Underweight | <5% |
| Healthy weight | 5% – 85% |
| At risk of overweight | 85% – 95% |
| Overweight | >95% |
Risks Associated with Obesity
Cardiovascular Disease Obesity significantly increases the risk of heart disease, high blood pressure, stroke, and abnormal cholesterol levels. Excess weight puts additional strain on the heart and blood vessels, while also promoting inflammation and insulin resistance that contribute to cardiovascular problems.
Type 2 Diabetes Obesity is one of the strongest risk factors for developing type 2 diabetes. Excess body fat, particularly around the abdomen, makes cells more resistant to insulin, forcing the pancreas to work harder and eventually leading to blood sugar control problems.
Respiratory Issues Adults with obesity often experience sleep apnea, where breathing repeatedly stops and starts during sleep, leading to poor sleep quality and daytime fatigue. They may also have reduced lung capacity and increased difficulty breathing during physical activity.
Joint Problems Extra weight puts additional stress on weight-bearing joints like knees, hips, and ankles, leading to increased wear and tear, arthritis, and chronic pain. This can significantly impact mobility and quality of life.
Cancer Risk Obesity is linked to increased risk of several cancers, including breast, colon, endometrial, kidney, and liver cancers. The mechanisms involve hormonal changes, chronic inflammation, and altered immune function.
Mental Health Adults with obesity face higher rates of depression, anxiety, and low self-esteem, often compounded by social stigma and discrimination. This can create a cycle where emotional distress contributes to further weight gain.
Other Health Issues Additional risks include fatty liver disease, gallbladder disease, kidney disease, pregnancy complications, and reduced fertility in both men and women.
Risks Associated with Childhood Obesity
Immediate Health Consequences Children with obesity may develop high blood pressure, high cholesterol, and early signs of type 2 diabetes – conditions once considered primarily adult diseases. They’re also more likely to experience breathing problems, joint pain, and fatty liver disease.
Psychological and Social Impact Children with obesity often face bullying, social isolation, and discrimination, leading to lower self-esteem, depression, and anxiety. These experiences can affect their academic performance and social development.
Sleep Disorders Like adults, children with obesity are at higher risk for sleep apnea and other sleep disturbances, which can affect their growth, cognitive development, and behavior.
Early Puberty Obesity in children, particularly girls, is associated with earlier onset of puberty, which can lead to psychological challenges and may affect long-term health outcomes.
Long-term Consequences Perhaps most concerning is that childhood obesity often persists into adulthood. Children with obesity are much more likely to become adults with obesity, carrying forward all the associated health risks. Early obesity can also lead to more severe adult obesity and earlier onset of related diseases.
Metabolic Programming Obesity during childhood and adolescence can affect how the body processes food and stores fat throughout life, potentially making weight management more challenging in adulthood.
Reduced Life Expectancy Studies suggest that severe childhood obesity may reduce life expectancy, with some research indicating it could shorten lifespan by several years.
The good news is that many of these risks can be reduced or reversed through healthy lifestyle changes, including improved diet, increased physical activity, and appropriate medical care when needed. Early intervention is particularly important for children, as establishing healthy habits during childhood can have lifelong benefits.
Ponderal Index
The Ponderal Index (PI) is an alternative body measurement that relates weight to height, similar to BMI but with a different mathematical approach. It’s calculated as weight divided by height cubed (kg/m³), rather than height squared like BMI.
Metric units:
Imperial units:
Key Characteristics: The ponderal index was designed to better account for the relationship between body weight and height, particularly for very tall or very short individuals. Since it uses height cubed rather than squared, it theoretically provides a more accurate assessment across different body sizes and proportions.
Primary Uses: PI is most commonly used in pediatric medicine, particularly for assessing newborns and infants. It’s considered useful for evaluating whether a baby is appropriately grown for their gestational age and can help identify infants who may be small-for-gestational-age or large-for-gestational-age.
Advantages Over BMI: For very tall or very short people, the ponderal index may provide a more accurate reflection of body composition than BMI. This is because BMI can sometimes overestimate obesity in tall people and underestimate it in short people, while PI’s cubic relationship with height may correct for this bias.
Normal Ranges: For adults, a typical ponderal index ranges from about 11-15 kg/m³, though specific cutoff points for health classifications aren’t as well-established as they are for BMI. For newborns, values typically range from 20-30 kg/m³.
Limitations: Despite its theoretical advantages, the ponderal index hasn’t gained widespread adoption in clinical practice. Like BMI, it still doesn’t distinguish between muscle and fat mass, and there’s less research establishing clear health risk categories. BMI remains the preferred screening tool for most adult populations due to its extensive validation and established clinical guidelines.
The ponderal index represents an interesting alternative approach to body composition assessment, but its practical application remains primarily in specialized areas like neonatal care.