Body mass index: How we calculate
How we calculate
BMI = weight in kilograms divided by height in metres squared. CDC adult categories use BMI < 18.5, 18.5 ≤ BMI < 25, 25 ≤ BMI < 30 and BMI ≥ 30.
BMI is a screening measure, not a diagnosis. These adult categories do not apply below age 20 or to weight assessment during pregnancy.
Worked example
An adult aged 30 weighs 70 kg and is 175 cm, or 1.75 m, tall. BMI = 70 / 1.75² ≈ 22.86, within 18.5 ≤ BMI < 25. The category is a screening reference, not a diagnosis or a body-composition assessment.