BMI Calculator
BMI is a screening number, not a diagnosis. It compares your weight to your height and places you in a broad band, which is useful for spotting a trend over years but blunt for any single person. This calculator gives you the value and the WHO category, and the notes below explain where it misleads.
Inputs
Result
22.9
Category: Normal weight
How it works
BMI = weight (kg) ÷ height (m)²
- 1Height in metres = 175 ÷ 100 = 1.75
- 2BMI = 70 ÷ 3.0625 = 22.9
How the bmi calculator works
BMI = weight in kilograms ÷ height in metres squared. For imperial units: 703 × pounds ÷ inches².
WHO bands: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30 and above obese. Asian population guidelines shift the overweight threshold down to about 23.
Because height is squared, BMI systematically reads slightly high for tall people and slightly low for short people — a known limitation of the formula, not an error in your measurement.
Worked example: 78 kg at 1.75 m
- Height squared: 1.75 × 1.75 = 3.0625.
- BMI = 78 ÷ 3.0625 = 25.5 — just inside the overweight band.
- Reaching a BMI of 24.9 would mean 76.3 kg, a loss of about 1.7 kg.
- The same person carrying 12% body fat would be muscular, not overweight, despite the identical BMI.
- In imperial: 172 lb at 69 in gives 703 × 172 ÷ 4,761 = 25.4.
Common mistakes to avoid
Treating BMI as a body composition measure
It cannot distinguish muscle from fat. Trained athletes routinely score in the overweight band while carrying low body fat.
Using adult bands for children
Children and teenagers are assessed on age-and-sex percentile charts, not fixed cut-offs. An adult BMI category is meaningless under 18.
Reacting to a single reading
Weight fluctuates 1–2 kg daily with hydration, food and salt. Compare weekly averages, not individual mornings.
Frequently asked questions
What is a healthy BMI?
18.5 to 24.9 by WHO bands, though many Asian guidelines use 18.5 to 22.9 because cardiometabolic risk rises at a lower BMI in those populations.
Is BMI accurate for athletes?
No. Muscle is denser than fat, so a lean, muscular person can register as overweight. Body fat percentage or waist-to-hip ratio is more informative.
Does BMI differ by sex?
The formula and the bands do not, even though women naturally carry more essential body fat. That is one reason body fat measures are preferred for individuals.
What is a better measure than BMI?
Waist circumference and waist-to-hip ratio capture abdominal fat, which drives most of the metabolic risk. Combining BMI with waist measurement is stronger than either alone.
How much weight change moves my BMI by one point?
Roughly your height in metres squared, in kilograms. At 1.75 m, about 3 kg shifts BMI by one point.
Learn more
How to Calculate BMI (and What It Actually Tells You)
The BMI formula, worked examples, and where the number falls short.
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