How to use this calculator
Enter age, weight and height. For imperial measurements use total inches: 5 feet 9 inches is 69 inches. Switching units converts your values. Read the result as a screening measure alongside other health information, rather than a diagnosis.
The math behind it
BMI = weight in kilograms / (height in meters)² 1 lb = 0.45359237 kg; 1 in = 2.54 cm
A worked example
An adult weighing 70 kg at 175 cm has BMI 70 / 1.75² ≈ 22.86 kg/m², within the CDC healthy-weight screening category.
Assumptions & precision
CDC adult categories apply from age 20: below 18.5 underweight; 18.5 to below 25 healthy weight; 25 to below 30 overweight; 30 or above obesity. Categories use unrounded values; the number displays two decimals. BMI does not distinguish muscle, bone and fat. Not for pregnancy or child growth assessment. Input bounds of age 20–120, weight 20–500 kg and height 100–250 cm are tool limits, not definitions of health. Inputs are not stored or sent to a server.
A common question
Is BMI a measure of body fat?
No. It compares weight with height and cannot identify how much weight is muscle or fat. A health professional can interpret it alongside medical history, measurements and other findings.