The Body Mass Index (BMI) Calculator helps you quickly find your BMI value and understand your weight category based on your age. You can switch between Metric and Other Units for easy conversion. Along with BMI, the calculator also measures the Ponderal Index to give you a clearer view of your overall body composition.

BMI introduction

Body Mass Index (BMI) is a numerical measurement of a person’s leanness or fatness in relation to their height and weight. It helps to estimate whether someone maintains a healthy weight for their body size. BMI is widely used as a screening tool rather than a diagnostic measure, helping doctors and individuals determine whether additional assessments or lifestyle changes might be necessary.

The value obtained from BMI calculations categorizes individuals as underweight, normal weight, overweight, or obese. These categories can differ slightly across regions, age groups, and populations, but they serve as a general guideline for public health and clinical research.

Although BMI has its limitations—it cannot directly measure body fat—it remains a valuable indicator of potential health risks linked to underweight or overweight conditions.

BMI Table for Adults

The World Health Organization (WHO) defines standard BMI ranges for adults aged 20 years or older. These classifications are used globally for both men and women.

These ranges are designed to provide a consistent framework for assessing health risks related to body weight. However, the interpretation of BMI should consider individual factors such as age, muscle mass, and overall body composition.

BMI Chart for Adults

The WHO BMI chart visually demonstrates how height and weight correspond to BMI categories.

The chart is divided by major categories (underweight, normal, overweight, obese), with dashed lines marking subcategories such as mild or severe obesity.

This visual guide helps individuals quickly determine their BMI zone and understand how minor changes in weight or height can shift their health classification.

BMI Table for Children and Teens (Ages 2–20)

Because children and adolescents are still growing, BMI must be evaluated differently from adults. The Centers for Disease Control and Prevention (CDC) uses BMI-for-age percentiles to compare a child’s weight with others of the same age and sex.

These percentiles consider growth patterns, puberty development, and individual differences. A pediatrician should interpret BMI for children and teens to determine if weight changes are due to natural growth or potential health risks.

BMI Chart for Children and Teens

The CDC growth charts—separate for boys and girls—illustrate BMI changes throughout childhood and adolescence. Because body composition shifts during puberty, BMI percentiles offer a more accurate picture of whether a young person’s weight aligns with healthy development milestones.

Risks Associated with Being Overweight

Being overweight or obese can increase the risk of numerous chronic diseases and medical conditions. According to the CDC and NHS UK, these include:

• High blood pressure (hypertension)

• High LDL cholesterol (“bad” cholesterol) and low HDL (“good”) cholesterol

• Type 2 diabetes

• Coronary heart disease

• Stroke

• Gallbladder disease

• Osteoarthritis, caused by extra strain on joints

• Sleep apnea and respiratory issues

• Certain cancers, such as breast, colon, kidney, and liver cancer

• Depression and anxiety

• Reduced quality of life and mobility

• Higher overall mortality risk

Excess body fat—especially around the abdomen—contributes to metabolic changes that increase inflammation, insulin resistance, and cardiovascular risk.

Maintaining a BMI below 25 kg/m² is generally linked with lower risk, but individual health should always be assessed through a combination of BMI, diet, physical activity, and medical evaluation.

Risks Associated with Being Underweight

Being underweight can also lead to significant health problems. Insufficient body fat and muscle mass can weaken the immune system and increase the likelihood of other health complications, including:

• Malnutrition and vitamin deficiencies

• Anemia, due to low red blood cell count

• Weakened bones (osteoporosis)

• Decreased immune function

• Growth and developmental issues (especially in children and teens)

• Menstrual irregularities or infertility in women

• Increased surgical complications

• Fatigue and low body temperature

• Higher overall mortality risk

In some cases, being underweight may indicate underlying health issues such as thyroid disorders, digestive diseases, or eating disorders like anorexia nervosa. If the cause of weight loss is unclear, a medical assessment is strongly advised.

Limitations of BMI

Although BMI is widely recognized, it has several important limitations. It measures total body weight, not body composition, meaning it cannot differentiate between fat mass, muscle, and bone density.

In Adults

BMI does not always represent health accurately because it cannot account for variations in muscle and fat distribution. For example:

• Athletes or muscular individuals may have a high BMI but low body fat.

• Older adults may have normal BMI yet higher fat percentage due to muscle loss.

• Women tend to have more body fat than men of the same BMI.

• Different ethnic groups may have varying health risks at the same BMI level.

According to health organizations like the CDC, BMI should be used as a general screening tool, not a diagnostic standard. It provides a useful estimate but should be interpreted alongside other measures such as waist circumference, cholesterol levels, and blood sugar.

In Children and Adolescents

BMI accuracy in youth is influenced by growth rate, sexual maturity, and height variations. It’s a better indicator of excess fat in obese children than in those who are slightly overweight. For lean children, BMI differences often reflect muscle and bone development rather than unhealthy fat levels.

Despite these limitations, BMI remains a practical tool for identifying trends in population health and guiding personal health awareness.

BMI and Age

The relationship between BMI and health changes with age.

• Younger adults may maintain a lower BMI naturally due to higher metabolism and activity levels.

• Older adults often carry more fat even at a normal BMI because of muscle loss.

• Middle-aged adults tend to experience gradual increases in BMI, often linked to lifestyle and hormonal changes.

While BMI helps track these shifts, other health factors—such as blood pressure, fitness level, and diet quality—are equally important to monitor over time.

How to Maintain a Healthy BMI

Maintaining a healthy BMI involves balancing calorie intake with physical activity and choosing nutrient-rich foods that support overall wellbeing. Trusted health authorities like the British Nutrition Foundation and NHS recommend:

• Eating balanced meals rich in vegetables, fruits, lean proteins, and whole grains

• Limiting processed foods and sugary beverages

• Engaging in regular exercise, at least 150 minutes of moderate activity weekly

• Getting adequate sleep and managing stress

• Monitoring weight changes gradually rather than obsessively

Small, consistent lifestyle choices are more effective for long-term weight control than extreme diets or rapid weight loss programs.

You can easily monitor your progress using a BMI Calculator, which helps you understand where you stand and track improvements over time.

BMI Formula

The BMI calculation differs slightly depending on the measurement system used.

US Customary Units:

BMI=703×weight (lbs)height (in)2BMI = 703 \times \frac{\text{weight (lbs)}}{\text{height (in)}^2}

BMI=703×height (in)2weight (lbs)

Metric Units:

BMI=weight (kg)height (m)2BMI = \frac{\text{weight (kg)}}{\text{height (m)}^2}

BMI=height (m)2weight (kg)

For example, a person weighing 160 lbs (72.5 kg) and standing 5’10” (1.78 m) tall would have a BMI of approximately 23.0, which falls into the normal category.

BMI and Overall Health

While BMI remains a key public health tool, it should never be viewed in isolation. A comprehensive understanding of health requires evaluating body composition, blood biomarkers, and lifestyle factors.

For most people, maintaining a BMI between 18.5 and 24.9 is associated with:

• Better heart and metabolic health

• Increased energy levels

• Lower risk of chronic illness

• Improved mental and emotional wellbeing

Still, BMI’s greatest value lies in awareness—helping individuals and professionals recognize potential risks early and make informed lifestyle decisions.