BMI Calculator

What Is BMI (Body Mass Index)?

Body Mass Index (BMI) is a simple numerical measure that uses your height and weight to estimate whether you fall within a healthy weight range. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI has become one of the most widely used screening tools for assessing weight-related health risks in adults.

BMI does not measure body fat directly. Instead, it provides a quick, inexpensive, and easy-to-perform indicator that correlates with more direct measures of body fat, such as underwater weighing or dual-energy X-ray absorptiometry (DEXA). Healthcare professionals, public health agencies, and insurance companies around the world use BMI as a first-line screening method to identify individuals who may be at increased risk for weight-related conditions such as heart disease, type 2 diabetes, high blood pressure, and certain cancers.

While BMI is not a perfect measure of health — it does not account for muscle mass, bone density, age, sex, or ethnic differences — it remains a valuable starting point for conversations about weight and health between patients and their healthcare providers. Understanding your BMI can help you make informed decisions about nutrition, physical activity, and overall wellness.

The BMI Formula

BMI is calculated by dividing a person's weight by the square of their height. The formula differs slightly depending on whether you are using metric or imperial units:

Example Calculations

Metric example: A person who weighs 70 kg and stands 1.75 m tall would have a BMI of:

• BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9

Imperial example: A person who weighs 160 lbs and is 5 feet 10 inches tall (70 inches total) would have a BMI of:

• BMI = 703 × 160 / (70 × 70) = 112,480 / 4,900 = 23.0

Both examples result in a BMI within the normal range (18.5–24.9), indicating a healthy weight for their height. The multiplication factor of 703 in the imperial formula is a conversion constant that accounts for the difference between pounds/inches and kilograms/meters.

BMI Categories and What They Mean

The World Health Organization and the CDC classify BMI into the following standard categories for adults aged 20 and older:

Underweight: BMI Below 18.5

A BMI below 18.5 indicates that a person may be underweight. Being underweight can be associated with health problems such as weakened immune function, nutritional deficiencies, fragile bones (osteoporosis), fertility issues, and increased susceptibility to infection. Common causes of being underweight include high metabolism, excessive physical activity, illness, eating disorders, or simply not consuming enough calories.

If your BMI falls in this range, it is important to speak with a healthcare provider. They can help determine whether an underlying medical condition is contributing to low weight and recommend an appropriate plan for reaching a healthier weight through nutrient-dense foods and balanced meals.

Normal Weight: BMI 18.5 – 24.9

A BMI between 18.5 and 24.9 is considered the healthy range for most adults. People in this range generally have the lowest risk for weight-related health problems. However, a normal BMI does not guarantee good health — factors such as diet quality, physical activity level, genetics, smoking status, and stress all play important roles in overall wellness.

Maintaining a BMI within this range through balanced nutrition and regular exercise is one of the best ways to support long-term health and reduce your risk of chronic disease.

Overweight: BMI 25 – 29.9

A BMI between 25 and 29.9 places a person in the overweight category. Being overweight increases the risk for a variety of health conditions, including cardiovascular disease, type 2 diabetes, sleep apnea, joint problems, and certain types of cancer. However, the degree of risk varies from person to person based on additional factors such as waist circumference, family history, and lifestyle habits.

For people in the overweight category, even modest weight loss of 5% to 10% of total body weight can produce meaningful health benefits, including lower blood pressure, improved cholesterol levels, and better blood sugar control.

Obese: BMI 30 and Above

A BMI of 30 or higher classifies a person as obese. Obesity is further divided into three classes: Class I (BMI 30–34.9), Class II (BMI 35–39.9), and Class III or severe obesity (BMI 40 or above). Obesity is associated with significantly increased risk for serious health conditions, including heart disease, stroke, type 2 diabetes, certain cancers, osteoarthritis, and mental health disorders such as depression.

Treatment approaches for obesity typically include dietary changes, increased physical activity, behavioral therapy, and in some cases medication or surgical interventions. Working with a healthcare team can help develop a personalized and sustainable plan.

BMI Chart for Adults

A BMI chart provides a quick visual reference for finding your BMI based on your height and weight. Below is a summary of BMI values at common heights and weights. Each cell shows the approximate BMI value, and the color-coded categories make it easy to identify where you fall.

To use the chart, find your height in the left column and then move across the row to find your weight. The number where they intersect is your approximate BMI. Here are some reference points at common heights:

BMI Reference at 5'4" (163 cm)

• 110 lbs (50 kg): BMI 18.9 — Normal
• 130 lbs (59 kg): BMI 22.3 — Normal
• 150 lbs (68 kg): BMI 25.7 — Overweight
• 180 lbs (82 kg): BMI 30.9 — Obese

BMI Reference at 5'9" (175 cm)

• 125 lbs (57 kg): BMI 18.5 — Normal (lower boundary)
• 150 lbs (68 kg): BMI 22.1 — Normal
• 170 lbs (77 kg): BMI 25.1 — Overweight
• 200 lbs (91 kg): BMI 29.5 — Overweight
• 205 lbs (93 kg): BMI 30.3 — Obese

BMI Reference at 6'0" (183 cm)

• 136 lbs (62 kg): BMI 18.4 — Underweight
• 140 lbs (64 kg): BMI 19.0 — Normal
• 170 lbs (77 kg): BMI 23.1 — Normal
• 200 lbs (91 kg): BMI 27.1 — Overweight
• 225 lbs (102 kg): BMI 30.5 — Obese

Limitations of BMI

While BMI is a useful and widely accepted screening tool, it has several well-documented limitations that are important to understand:

Does Not Distinguish Between Fat and Muscle

BMI uses only weight and height, so it cannot differentiate between body fat, muscle mass, bone density, and water weight. Athletes, bodybuilders, and people with high muscle mass may have a BMI in the overweight or even obese range despite having a low body fat percentage and being in excellent physical condition. Conversely, an older person with low muscle mass may have a normal BMI but carry an unhealthy amount of body fat.

Does Not Account for Fat Distribution

Where fat is stored in the body matters for health risk. Visceral fat (fat around the abdominal organs) is more strongly associated with cardiovascular disease and metabolic syndrome than subcutaneous fat (fat under the skin). Two people with the same BMI can have very different risk profiles depending on where they carry their weight. Waist circumference and waist-to-hip ratio are complementary measurements that can help address this limitation.

Age, Sex, and Ethnicity Differences

BMI does not account for age-related changes in body composition, differences in body fat percentage between men and women, or variations across ethnic groups. For example, Asian populations may face higher health risks at lower BMI thresholds, and some health organizations recommend using a BMI of 23 (rather than 25) as the overweight cutoff for people of Asian descent. Similarly, women typically have more body fat than men at the same BMI level.

Not Suitable as a Sole Diagnostic Tool

BMI should be used as one component of a comprehensive health assessment, not as the only measure. Blood pressure, cholesterol levels, blood sugar, physical fitness, family history, diet quality, and mental health all contribute to a person's overall health status and should be considered alongside BMI.

Achieving and Maintaining a Healthy Weight

If your BMI indicates that you are outside the healthy range, there are evidence-based strategies you can adopt to move toward a healthier weight:

1. Focus on Nutrition Quality

Rather than following extreme diets, focus on whole, nutrient-dense foods: vegetables, fruits, whole grains, lean proteins, nuts, and seeds. Reduce consumption of processed foods, sugary beverages, and foods high in saturated and trans fats. Pay attention to portion sizes and try to eat mindfully, savoring each meal rather than eating in front of screens.

2. Increase Physical Activity

The CDC recommends at least 150 minutes of moderate-intensity aerobic activity (such as brisk walking or cycling) per week, plus muscle-strengthening activities on two or more days per week. If you are currently sedentary, start slowly and gradually increase duration and intensity. Find activities you enjoy to make exercise sustainable.

3. Set Realistic Goals

Healthy weight loss is typically 1 to 2 pounds (0.5 to 1 kg) per week. Setting small, achievable goals — like losing 5% of your body weight over several months — is more sustainable and produces measurable health benefits. Avoid crash diets or extreme caloric restriction, which can lead to muscle loss, nutritional deficiencies, and weight regain.

4. Prioritize Sleep and Stress Management

Poor sleep and chronic stress disrupt hormones that regulate hunger and metabolism, including cortisol, leptin, and ghrelin. Aim for 7 to 9 hours of quality sleep per night and incorporate stress reduction practices such as meditation, deep breathing exercises, yoga, or spending time in nature.

5. Seek Professional Support

If you are struggling with weight management, consider working with healthcare professionals such as a registered dietitian, personal trainer, or your primary care physician. They can provide personalized guidance, identify underlying health conditions that may affect weight, and help create a sustainable plan tailored to your needs.

BMI for Children and Teens

BMI is calculated the same way for children and teens as for adults (weight divided by height squared), but the interpretation is different. Because body composition changes naturally as children grow and differs between boys and girls, BMI for children and teens is age- and sex-specific and is expressed as a percentile relative to other children of the same age and sex.

BMI-for-Age Percentile Categories

The CDC uses the following percentile ranges for children and teens aged 2 to 19:

• Underweight: Below the 5th percentile
• Healthy weight: 5th percentile to below the 85th percentile
• Overweight: 85th percentile to below the 95th percentile
• Obese: 95th percentile or above

Why Percentiles Instead of Fixed Ranges?

Children's body fat levels change naturally as they grow. A 7-year-old and a 15-year-old with the same BMI number may be in very different health categories because normal body fat percentages differ by age. Similarly, girls and boys have different body composition patterns. Using age- and sex-specific percentiles ensures that BMI is interpreted in the proper developmental context.

When to Talk to a Pediatrician

If your child's BMI percentile falls outside the healthy range, consult their pediatrician. The doctor can assess whether the child's weight is appropriate by considering growth patterns over time, physical activity level, family history, and other health indicators. Avoid putting children on restrictive diets without medical guidance, as proper nutrition is essential for healthy growth and development.