Understanding your weight in relation to your height can be a useful first step toward making informed health decisions. A BMI Calculator gives you a quick estimate of your body mass index using your height and weight.
Your BMI result can help you identify the adult weight category that applies to you. However, BMI does not directly measure body fat or diagnose a medical condition. It should be considered alongside your medical history, body composition, blood pressure, laboratory results, lifestyle, and advice from a qualified healthcare professional.
Use the calculator below to estimate your BMI and then continue reading to understand what the result may mean.
Table of Contents
What Is BMI?
Body mass index, commonly called BMI, is a calculation that compares your weight with your height. It provides a standardized number that healthcare professionals and public-health organizations can use as a weight-status screening measure.
BMI is quick, inexpensive, and easy to calculate. For individual health decisions, however, the result should be evaluated with other information, such as blood pressure, cholesterol levels, physical examination findings, medical history, and health behaviors.
BMI does not tell you exactly how much body fat you have. It also cannot determine whether your weight comes primarily from fat, muscle, bone, or another part of your body composition.
Free BMI Calculator for U.S. Adults
Use the BMI Calculator below to estimate your BMI with U.S. customary or metric measurements.
Enter your measurements
For U.S. customary units, enter:
- Your height in feet and inches
- Your weight in pounds
For metric units, enter:
- Your height in centimeters
- Your weight in kilograms
This adult calculator is intended for people who are 20 years of age or older. Children and teenagers between ages 2 and 19 require a child-specific calculator that interprets BMI using age- and sex-specific percentiles.
How to Use the BMI Calculator
Follow these steps to obtain a more reliable result:
- Select U.S. customary or metric units.
- Enter your current height.
- Enter your current weight.
- Check that the measurements are accurate.
- Select the calculate button.
- Review your BMI number and adult BMI category.
Measure your weight without heavy clothing when possible. Measure your height while standing upright without shoes, with your feet flat and your head level.
Remember that a BMI category is not a diagnosis. It is a starting point for understanding your weight in relation to your height.
How Is BMI Calculated?
BMI is calculated using your weight and the square of your height. The formula differs slightly depending on whether you use U.S. customary or metric measurements.
BMI formula using pounds and inches
BMI = weight in pounds ÷ height in inches² × 703
For example, consider an adult who weighs 165 pounds and is 5 feet 6 inches tall.
First, convert the height into inches:
5 feet 6 inches = 66 inches
Then calculate:
BMI = 165 ÷ 66² × 703
BMI = 26.6
Based on standard adult categories, a BMI of 26.6 is within the overweight category. The category alone does not determine whether that individual has a health condition.
BMI formula using kilograms and meters
BMI = weight in kilograms ÷ height in meters²
For example, consider an adult who weighs 70 kilograms and is 1.75 meters tall:
BMI = 70 ÷ 1.75²
BMI = 22.9
A BMI of 22.9 is within the standard healthy-weight category for adults.
Adult BMI Chart and Categories
For U.S. adults aged 20 and older, the Centers for Disease Control and Prevention uses the following BMI categories. The categories apply regardless of an adult’s age or sex.
| Adult BMI | Weight category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0 or higher | Obesity |
| 30.0–34.9 | Class 1 obesity |
| 35.0–39.9 | Class 2 obesity |
| 40.0 or higher | Class 3 obesity |
These categories are screening classifications. They do not explain why someone has a particular weight or determine that person’s complete health status.
What Does Your BMI Result Mean?
Your BMI result identifies a general weight category based on your height and weight. Understanding that category may help you decide whether to discuss your weight, nutrition, physical activity, or overall health with a healthcare professional.
BMI below 18.5
A BMI below 18.5 falls within the underweight category. A lower BMI can have many possible explanations, including natural body size, recent weight loss, nutrition concerns, illness, medication effects, or other health circumstances.
Consult a healthcare professional when a low result is unexpected or accompanied by weakness, fatigue, appetite changes, digestive problems, or unexplained weight loss.
BMI between 18.5 and 24.9
A BMI between 18.5 and 24.9 falls within the standard healthy-weight category. This category may be reassuring, but it does not guarantee that every aspect of your health is optimal.
Blood pressure, cholesterol, blood sugar, physical activity, nutrition, sleep, smoking status, medical history, and waist circumference can provide additional information.
BMI between 25.0 and 29.9
A BMI between 25.0 and 29.9 falls within the overweight category. This result does not automatically mean that you have excess body fat or a medical condition.
People with greater muscle mass may have a higher BMI even when their body-fat level is relatively low. A healthcare professional can consider your body composition, waist measurement, lifestyle, and other health indicators.
BMI of 30.0 or higher
A BMI of 30.0 or higher falls within the obesity category, which is divided into three classes. Higher weight can be associated with health risks, but BMI remains a screening measurement rather than a diagnosis.
A healthcare professional can help assess your individual circumstances without relying on BMI alone.
Important Limitations of a BMI Calculator
A BMI Calculator is convenient, but it cannot provide a complete picture of your health.
BMI does not distinguish among:
- Body fat
- Muscle mass
- Bone mass
- Body-fat distribution
- Fluid weight
- Individual body composition
It also does not show where fat is stored in the body. Two people with the same height, weight, and BMI can have significantly different levels of muscle and body fat.
BMI and muscular adults
Athletes, bodybuilders, and physically active adults may have more muscle than the average person. Because muscle contributes to total body weight, a muscular person may receive an overweight or obesity-category result despite having relatively low body fat.
BMI during pregnancy
An ordinary adult BMI calculation is not designed to interpret expected weight changes during pregnancy. Pregnant individuals should follow personalized guidance from their obstetrician, midwife, or another qualified maternity-care professional.
BMI and body-fat distribution
BMI cannot identify where your body stores fat. Healthcare professionals may consider waist circumference and other assessments when evaluating weight-related health risks.
Is BMI Different for Men and Women?
The standard adult BMI formula and category ranges are generally the same for adult men and women aged 20 and older.
However, BMI does not account for differences in muscle mass, body-fat percentage, fat distribution, hormonal health, pregnancy, menopause, medical history, or fitness level. This is why two adults with the same BMI may have different health needs.
BMI should not be used to compare your appearance or health with another person.
Does Age Affect BMI?
Standard adult BMI categories are used for people aged 20 and older. The calculation does not create separate adult categories based on age.
Children and teenagers are different because their bodies are still growing. For people ages 2 through 19, BMI is interpreted through sex-specific BMI-for-age percentiles rather than the standard adult categories.
Parents and caregivers should not use an adult BMI Calculator to assess a child’s growth. A pediatric healthcare professional can interpret a child’s measurements within the context of growth patterns and overall development.
Factors to Consider Alongside BMI
Your BMI result becomes more meaningful when it is considered with other health information. Depending on your circumstances, a healthcare professional may review:
- Changes in your weight over time
- Waist circumference
- Blood pressure
- Cholesterol levels
- Blood glucose
- Medical and family history
- Eating patterns
- Physical activity
- Sleep habits
- Medications
- Muscle mass and body composition
- Physical examination findings
The CDC recommends considering BMI with factors such as medical history, health behaviors, examination results, and laboratory findings.
When Should You Talk to a Healthcare Professional?
Consider speaking with a qualified healthcare professional when:
- Your weight has changed unexpectedly.
- You are concerned about a very low or high BMI.
- You are pregnant or planning a pregnancy.
- You have a history of disordered eating.
- You have a chronic medical condition.
- You take medication that affects appetite or weight.
- You are an athlete with substantial muscle mass.
- Your BMI result conflicts with other health measurements.
- You want personalized weight-management guidance.
- Weight concerns are affecting your emotional well-being.
A registered dietitian may also help you develop an eating pattern that considers your health needs, food preferences, cultural background, schedule, and budget.
Healthy Ways to Support Weight Management
A sustainable approach to health usually focuses on repeatable habits rather than rapid or extreme changes.
Build balanced meals
Choose a variety of foods that provide protein, fiber, carbohydrates, healthy fats, vitamins, and minerals. A balanced meal might include vegetables or fruit, a protein source, and a whole-grain or other high-fiber carbohydrate.
Avoid labeling individual foods as completely “good” or “bad.” Your overall eating pattern is more important than one meal.
Choose enjoyable physical activity
Walking, swimming, cycling, dancing, recreational sports, resistance training, and active household tasks can all contribute to regular movement.
Begin at a level that matches your health and current ability. People with medical conditions, injuries, or significant mobility concerns should obtain personalized advice before starting a demanding exercise program.
Protect your sleep
Regular sleep can support energy, mood, appetite awareness, and your ability to stay physically active. Focus on a consistent schedule and a relaxing bedtime routine.
Manage stress constructively
Stress can affect appetite, sleep, motivation, and daily routines. Consider practical strategies such as breathing exercises, time outdoors, journaling, social connection, counseling, or reducing unnecessary commitments.
Track progress beyond the scale
Body weight is only one possible measurement. You may also notice improvements in:
- Energy
- Strength
- Endurance
- Sleep
- Mobility
- Blood pressure
- Laboratory results
- Confidence with healthy routines
Avoid extreme diets, unverified supplements, or programs promising rapid and effortless weight loss. Seek professional guidance when you need a plan designed around a health condition.
Conclusion
A BMI Calculator offers a simple way to compare your weight with your height and identify your standard adult BMI category. It can be a useful starting point, especially when tracking general changes over time.
However, your BMI number does not define your health, appearance, ability, or personal worth. It cannot directly measure body fat, muscle mass, fitness, nutrition, or medical well-being.
Use your result as one piece of information. For a more complete assessment, consider your medical history, lifestyle, laboratory results, waist measurement, body composition, and guidance from a qualified healthcare professional.
FAQs
Q1: What is considered a healthy BMI?
A1: For adults aged 20 and older, a BMI between 18.5 and 24.9 is categorized as healthy weight. However, BMI is only a screening measurement and should be interpreted with other health information.
Q2: Is a BMI Calculator accurate?
A2: A BMI Calculator can accurately perform the mathematical BMI formula when the height and weight entered are correct. However, the result cannot directly measure body fat, muscle mass, bone density, fat distribution, or overall health.
Q3: Does BMI measure body fat?
A3: No. BMI uses height and weight to estimate weight status, but it does not directly measure body fat. The CDC notes that BMI cannot distinguish among fat, muscle, and bone mass.
Q4: Is BMI calculated differently for men and women?
A4: The standard adult BMI formula and category ranges are the same for adult men and women. Individual body composition and health circumstances can still differ significantly.
Q5: Can athletes rely on BMI?
A5: Athletes can calculate BMI, but they should interpret the result carefully. Greater muscle mass may increase body weight and BMI without indicating a high level of body fat.
Q6: Should children use an adult BMI Calculator?
A6: No. Children and teenagers ages 2 through 19 should use a child and teen BMI calculator. Their results must be interpreted using BMI-for-age percentiles based on age and sex.
Q7: Can BMI diagnose obesity or another illness?
A7: BMI can place an adult within a screening category, but it is not intended to diagnose a disease or determine a person’s complete health status. A diagnosis requires an appropriate professional assessment.
Q8: How often should I calculate my BMI?
A8: There is usually no need to calculate BMI every day. Weight naturally fluctuates because of hydration, meals, hormones, and other factors. Discuss an appropriate monitoring schedule with your healthcare professional when you are actively managing a health condition.