BMI Calculator
0.0 BMI
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity | 30.0 and above |
How BMI Is Calculated
Body Mass Index uses the standard formula adopted by the World Health Organization and the CDC: BMI = weight in kilograms divided by height in meters squared (kg/m²). When you enter weight in pounds and height in feet and inches, this calculator converts to metric first (1 lb = 0.453592 kg, 1 in = 0.0254 m) and then applies the same formula, so US and metric entries always produce identical results for the same body size.
BMI Is a Screening Tool, Not a Diagnosis
BMI does not distinguish between muscle and fat, so very muscular people are often classified as "overweight" despite having low body fat, while older adults or those with little muscle mass can have a "normal" BMI while still carrying excess fat. If you want a more direct estimate of body composition, try the body fat calculator or the lean body mass calculator. The category ranges shown above are the standard WHO adult thresholds and are not adjusted for age, sex, or athletic build.
What BMI Prime Tells You
BMI Prime is your BMI divided by the upper limit of the normal range (25), so a value of 1.0 sits exactly at the normal/overweight boundary — useful for seeing at a glance how far above or below that line you fall. This tool is for general education only and isn't a substitute for a clinical assessment; talk to a doctor or registered dietitian about what a healthy weight looks like for you.
Frequently Asked Questions
What is considered a healthy BMI?
A BMI between 18.5 and 24.9 falls in the WHO/CDC 'normal weight' range for adults. Below 18.5 is classified as underweight, 25.0-29.9 as overweight, and 30.0 or above as obesity. These thresholds apply to adults generally and are not adjusted for age, sex, or muscle mass.
Why does BMI seem inaccurate for muscular or very lean people?
BMI only uses height and weight, so it can't tell muscle from fat. A muscular athlete can weigh enough to score 'overweight' on BMI while actually having very low body fat, and someone with little muscle can have a 'normal' BMI while carrying excess fat. For a composition-based estimate, the body fat calculator or lean body mass calculator gives a more direct picture.