DocomintBMI Calculator
Calculate Body Mass Index from weight and height, with the standard weight category.
What is a BMI Calculator?
BMI (Body Mass Index) divides weight by height squared to give a single screening number the WHO and most health guidelines still use as a first-pass check — it's fast to compute but doesn't distinguish muscle from fat, so an athletic person can register as "overweight" despite low body fat, which Body Fat Calculator addresses more directly.
How to use the BMI Calculator
- Enter your weight in kilograms and height in centimeters
- Press Calculate BMI
- Your BMI and weight category appear instantly, computed on your device
Formula
BMI = weight(kg) ÷ height(m)²
Height is squared and used as the divisor, which is why BMI changes so much between people of different heights even at the same weight.
Example
A 70kg person at 175cm has a BMI of 22.9 (70 ÷ 1.75²) — squarely in the "Normal weight" 18.5–24.9 range used by most standard BMI charts.
Common mistakes
- Entering height in centimeters without converting to meters for the mental-math version of the formula — this tool handles the conversion internally, so just enter cm directly.
- Treating a single BMI number as an individual health diagnosis rather than the population-level screening indicator it was designed as.
- Using the adult BMI categories for a child or teenager — pediatric BMI is interpreted against age- and sex-specific percentile charts, not these fixed adult ranges.
Frequently asked questions
What do the BMI categories mean?
Under 18.5 is classified Underweight, 18.5–24.9 Normal weight, 25–29.9 Overweight, and 30+ Obese — the WHO's standard adult categories, used as a first-pass screening tool rather than an individual health diagnosis.
Why doesn't BMI account for muscle mass?
BMI only uses weight and height — it can't distinguish a kilogram of muscle from a kilogram of fat, so a muscular, athletic person can register as "overweight" on BMI despite having low body fat. Body Fat Calculator gives a more direct read on body composition.
Does this work for children?
Not accurately — child and teen BMI is interpreted using age- and sex-specific percentile charts rather than the fixed adult category ranges (Underweight/Normal/Overweight/Obese) this tool uses. Use a pediatric growth chart for anyone under 20.
What's a healthy BMI range?
18.5–24.9 is classified "Normal weight" under the WHO's standard adult categories — used as a first-pass screening range rather than an individualized target, since BMI alone can't distinguish muscle from fat.
Is my numbers uploaded anywhere?
No — BMI Calculator runs entirely in your browser using JavaScript/WebAssembly. Your numbers is never sent to a server.