About this calculator
Body mass index (BMI) compares your weight with your height to screen for weight categories linked to health risks. It is the measure used by the World Health Organization, the CDC and most doctors' offices — not because it is perfect, but because it is quick, free and consistent enough to flag who should take a closer look.
BMI has known blind spots. It cannot tell muscle from fat, so muscular athletes often score "overweight" with low body fat, and older adults can score "healthy" while carrying little muscle. Treat your result as a screening signal, not a diagnosis — our Body Fat Calculator gives a fuller picture.
How to use it
- Choose imperial (pounds and total inches) or metric (kilograms and centimeters).
- Enter your weight and height — for imperial height, add feet × 12 plus inches (5 ft 10 in = 70).
- Read your BMI, its category, and the healthy weight range for your height.
The formula
The index divides weight by the square of height so that taller people are not automatically scored heavier. The categories are fixed worldwide: below 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30 and above obese.
Worked example
At 180 lb and 5 ft 10 in (70 in), BMI = 703 × 180 ÷ 70² = 25.8 — just inside the overweight band. The healthy range for 70 inches runs from about 129 lb to 174 lb. In metric, 80 kg at 180 cm gives a BMI of 24.7, the top of the healthy band.
Frequently asked questions
What is a healthy BMI?
For adults, 18.5 to 24.9 is the healthy range used by the WHO and CDC. Below 18.5 is underweight; 25–29.9 is overweight; 30+ is obese, subdivided into classes at 35 and 40. Children and teens use age- and sex-specific percentiles instead — adult cutoffs do not apply.
Why do athletes get high BMI scores?
Because BMI counts all weight the same, and muscle is denser than fat. A lean, muscular athlete at 6 ft and 220 lb scores a BMI of about 29.8 — "overweight" — despite very low body fat. Waist circumference and body-fat percentage are better measures for muscular builds.
Is BMI different for men and women?
The adult categories are the same for both sexes, which is one of BMI's simplifications: at the same BMI, women on average carry a few percentage points more body fat than men. Researchers have proposed sex- and ethnicity-specific cutoffs, but the standard thresholds remain the screening norm.
How much weight should I lose to reach a healthy BMI?
Use the healthy range shown for your height: the gap between your current weight and the top of the range is a reasonable first target. Sustainable loss is typically 0.5–1% of body weight per week; pair the target with the Calorie Calculator to translate it into a daily intake.