Guide
BMI Basics — What the Number Means (and Doesn’t)
BMI (body mass index) is a height-and-weight screening number used in many public-health charts. It is not a diagnosis, a body-fat test, or a fitness score. Use it as a conversation starter with a clinician when health decisions are on the line.
Updated September 15, 2026
What BMI is
Metric BMI = weight (kg) / [height (m)]². Imperial forms convert pounds and inches to the same ratio.
Standard adult categories (underweight, healthy weight, overweight, obesity) are population screening bands — individual health depends on many other factors.
How to use the calculator
Enter height and weight in the units the form shows (or switch units if offered).
Read the BMI value and the category label, then the interpretation tips on the page.
How to read the numbers
BMI does not measure muscle, bone density, or fat distribution. Athletes may land higher without excess fat; older adults may look “healthy” on BMI while carrying little muscle.
Small rounding in height can move BMI across a category boundary — treat edges carefully.
Common mistakes
Using BMI alone to set aggressive diet or training goals.
Mixing unit systems (cm with pounds, or inches with kilograms).
Applying adult charts to children without pediatric guidance.
Worked example
Someone 1.75 m tall weighing 70 kg has BMI = 70 / (1.75²) ≈ 22.9, often labeled a healthy-weight band on adult charts.
Try those inputs in the BMI Calculator, then change weight by a few kilograms to see how sensitive the score is.