BMI Calculator for Adults: Calculate and Understand Your Body Mass Index
Our free BMI calculator for adults gives you a quick way to compare your weight with your height. Enter feet, inches, and pounds for US measurements, or switch to centimeters and kilograms for metric measurements. The calculator returns your Body Mass Index, the standard adult BMI category, and an estimated healthy weight range for your height. No account is required, and the calculation runs in your browser.
BMI is best treated as a starting point, not a diagnosis or a complete report card on your health. It can help identify whether a follow-up conversation about weight and health may be useful, but it does not directly measure body fat, muscle, fitness, blood pressure, blood sugar, or cholesterol.[2] Use the result together with your health history and advice from a qualified healthcare professional.
What Is BMI?
Body Mass Index is a ratio of weight to height squared. Healthcare and public-health organizations use it as a fast, inexpensive screening measure for adults.[2] For people age 20 and older, the standard categories are the same for men and women:[1] underweight, healthy weight, overweight, and obesity. A BMI result describes a statistical range; it does not explain why someone has that result or determine their health by itself.
How to Use This Adult BMI Calculator
- Choose your units. Keep Imperial selected for pounds, feet, and inches, or switch to Metric for kilograms and centimeters.
- Enter your current height and weight. For the most consistent result, measure without shoes and use a reliable scale on a firm, level surface.
- Enter an age of 20 or older. This page uses adult BMI ranges. Children and teenagers need age- and sex-specific BMI percentiles rather than the adult chart.[2]
- Select Calculate BMI. Review the BMI number, category, estimated healthy weight range, and general wellness guidance.
- Recheck unusual results. Confirm your units and measurements before making any interpretation. A small height-entry error can noticeably change BMI.
How BMI Is Calculated
The calculator supports both common BMI formulas:
Metric formula
BMI = weight (kg) ÷ height² (m²)
US formula
BMI = 703 × weight (lb) ÷ height² (in²)
Example: an adult who weighs 170 pounds and is 5 feet 8 inches tall has a BMI of approximately 25.8. The calculator also reverses the formula using BMI values of 18.5 and 24.9 to estimate the healthy weight range for the entered height. That range is a mathematical reference, not a personalized target or treatment recommendation.
Adult BMI Chart and Healthy BMI Range
| Adult BMI | Category | How to interpret it |
|---|---|---|
| Below 18.5 | Underweight | A follow-up may help identify nutrition, medical, or other contributing factors. |
| 18.5 to 24.9 | Healthy weight | Within the standard healthy BMI range for adults.[1] |
| 25.0 to 29.9 | Overweight | Consider BMI alongside waist size, habits, fitness, and clinical markers. |
| 30.0 to 34.9 | Obesity, Class 1 | A clinician can provide an individualized health assessment. |
| 35.0 to 39.9 | Obesity, Class 2 | Professional assessment can help evaluate related risk factors.[3] |
| 40.0 or higher | Obesity, Class 3 | Seek individualized, respectful medical guidance. |
A healthy BMI for adults is generally 18.5 through 24.9. There is no separate standard adult BMI range for men: the calculation and category thresholds are the same for adult men and women.[1] However, people with the same BMI can have different amounts and distributions of muscle and body fat, so their broader health picture may be different.
What Is a Healthy Weight for My Height?
The “Healthy Weight Range” in your result estimates the weights that correspond to a BMI from 18.5 to 24.9 at your height. For example, the range changes with height because BMI divides weight by height squared. It should not be treated as a required goal. Pregnancy, fluid retention, major changes in muscle mass, certain medical conditions, and some stages of later life can make a general BMI-based range less informative.
BMI Limitations: What the Number Cannot Tell You
BMI does not distinguish fat mass from muscle, bone, or water.[2] A muscular athlete may have a high BMI without having excess body fat, while someone within the healthy BMI range may still have metabolic risk factors. BMI also cannot show where body fat is stored. Waist circumference, blood pressure, laboratory results, sleep, activity, medications, family history, and changes over time can add important context.
Population background and body composition may also affect how BMI relates to health risk. That is why the calculator avoids presenting the result as a medical diagnosis. If your BMI has changed unexpectedly, falls far outside the standard range, or conflicts with other health information, speak with a healthcare professional rather than relying on the number alone.
BMI for Children, Teens, and Pregnancy
This calculator is designed for adults age 20 and older. For ages 2 through 19, BMI must be interpreted using age- and sex-specific growth-chart percentiles.[2] Adult cutoffs should not be applied to a child or teenager.[2] BMI is also not interpreted in the usual way during pregnancy because expected weight gain and physiological changes require pregnancy-specific guidance. For date planning during pregnancy, you can use our pregnancy due date calculator, but medical questions should go to your prenatal-care professional.
How to Make Your BMI Result More Useful
- Look at the trend. Measurements taken consistently over time often provide more context than a single reading.
- Add other indicators. Discuss waist circumference, blood pressure, glucose, cholesterol, fitness, and family history with your clinician.
- Use sustainable habits. Focus on balanced meals, regular movement, adequate sleep, and realistic changes instead of chasing one number.
- Avoid self-diagnosis. Unexpected weight loss or gain can have many causes and deserves appropriate professional evaluation.
If you are planning daily nutrition, our calorie calculator can provide a separate energy estimate. You can also explore the healthy BMI guide for American adults for additional context. These tools are educational and do not replace care from a doctor or registered dietitian.
Frequently Asked Questions
What is a normal BMI for adults?
The standard healthy or “normal” BMI range for adults age 20 and older is 18.5 to 24.9. BMI is a screening measure, so other health information still matters.
Is the healthy BMI range different for men and women?
No. Standard adult BMI categories use the same cutoffs for men and women. Body composition can differ, however, which is one reason BMI should not be used alone.
Is BMI an accurate measure of body fat?
BMI does not measure body fat directly. It uses only height and weight, so it cannot distinguish muscle from fat or show fat distribution.
Can I use this calculator for a child or teenager?
No. Children and teens ages 2–19 require BMI-for-age percentiles based on age and sex. Use a pediatric calculator and discuss growth concerns with a healthcare professional.
Why does the calculator show a healthy weight range?
It calculates the weights at your entered height that correspond to adult BMIs of 18.5 and 24.9. It is a general reference range, not a personalized goal.
Health note: This calculator provides educational estimates only. It is not intended to diagnose a condition, assess an emergency, or replace professional medical advice.