Free BMI Calculator for Adults
Calculate your Body Mass Index using height and weight. See your adult BMI category, healthy weight range, and BMI Prime in seconds.
This calculator is for adults aged 20 and older. BMI is a screening measure, not a medical diagnosis. It may not accurately reflect health risk for athletes, pregnant people, children, older adults, or people with unusual muscle or body-fat distribution.
Calculate Your BMI
Your BMI Score
Adult BMI Category Chart
Standard adult BMI categories are a screening framework. They do not diagnose health status by themselves.
| BMI Range | Category | What it means | Practical next step |
|---|---|---|---|
| Below 18.5 | Underweight | Below the adult healthy-weight range. | Review nutrition, health history, and weight trend with a professional if concerned. |
| 18.5 to 24.9 | Healthy Weight | Within the standard adult healthy-weight range. | Maintain healthy habits and consider other markers like waist circumference. |
| 25.0 to 29.9 | Overweight | Above the adult healthy-weight range. | Review activity, nutrition, sleep, and metabolic risk factors. |
| 30.0 to 34.9 | Obesity Class I | Meets the BMI threshold for obesity. | Consider professional guidance for a safe, sustainable plan. |
| 35.0 to 39.9 | Obesity Class II | Higher BMI category associated with increased health risk. | Discuss risk factors and treatment options with a qualified clinician. |
| 40.0 and above | Obesity Class III | Highest standard adult BMI obesity class. | Medical evaluation can help identify safe and appropriate options. |
How Body Mass Index Works
BMI is simple, fast, and useful for screening. Its main weakness is that it cannot tell the difference between fat mass, lean muscle, bone density, and fluid weight.
What Is a BMI Calculator?
A BMI calculator estimates Body Mass Index from a person's height and weight. It is commonly used as a starting point for understanding whether an adult's weight is below, within, or above the standard healthy-weight range.
BMI Formula
Example Calculation
A person who is 175 cm tall and weighs 70 kg has a BMI of 70 / (1.75 x 1.75), which equals 22.9. That falls within the standard adult healthy-weight range.
Why BMI Is Useful
BMI is popular because it is fast, free, and easy to calculate. It can help people notice weight trends and discuss possible risk factors with a healthcare professional.
- Works with only height and weight.
- Useful for adult population-level screening.
- Gives a quick category for underweight, healthy weight, overweight, or obesity.
- Can be tracked over time to monitor broad weight changes.
Where BMI Falls Short
BMI should not be treated as a complete picture of health. A single BMI number can miss important differences between people.
- Does not separate fat mass from muscle mass.
- Does not show where body fat is stored.
- Can misclassify very muscular people.
- Adult cutoffs should not be used for children or teens.
- Pregnancy, age, ethnicity, and medical history can affect interpretation.
BMI vs. Other Health Measurements
For a fuller picture, BMI is often considered alongside waist circumference, waist-to-height ratio, blood pressure, cholesterol, blood glucose, health history, and physical exam findings. Body composition tools such as DEXA, skinfold measurement, and bioelectrical impedance can add more detail, but they are not always necessary for basic screening.
The practical takeaway is simple: use BMI as a starting point, not as the final answer. If your BMI result concerns you, the next step is not panic. The next step is better context.
Sources and Medical Note
Last updated: May 2026. This page is for general educational use and does not provide medical advice, diagnosis, or treatment.