BMI Calculator
Calculate Body Mass Index (BMI) and category.
A BMI calculator checks your body mass index from your height and weight. You enter two numbers and the tool returns a single score. That score places you in a weight range that health bodies use worldwide. It gives you a fast read on your weight status without charts or manual math.
How the BMI Calculator Works
The tool divides your weight by the square of your height. It then compares the result against standard ranges from the World Health Organization. You see your number and your category on the same screen. The whole check takes a few seconds.
The tool runs fully in your browser. It stores nothing and asks for no sign up. Your height and weight stay on your own device. You get a private result the moment you press the button.
What You Enter
- Your height in centimeters, or in feet and inches
- Your weight in kilograms, or in pounds
Use the Units menu to switch between metric and US units. Metric takes kilograms and centimeters, while US takes pounds, feet and inches. The tool converts US figures before it calculates, so the score comes out the same either way.
The Body Mass Index Formula
BMI Categories and What They Mean
- Underweight, below 18.5
- Healthy weight, 18.5 to 24.9
- Overweight, 25 to 29.9
- Obese, 30 and above
A higher band does not confirm poor health on its own. It signals that a closer look may help. A doctor can weigh your score against blood pressure, diet and family history before any advice. Use the band as a starting point rather than a verdict.
Why Your Score Matters
A score in the overweight or obese range links to higher odds of heart disease and type 2 diabetes. A score in the underweight range can point to weak bones or low energy stores. The number gives you an early prompt to act while change is still easy. Small steps in diet and activity often move it over time, and even a modest drop can lower those health risks.
BMI for Men, Women and Children
In adults the score reads the same way for men and women. Muscle and frame can push the number up in very fit people. A lifter may score high yet carry very little fat. The tool flags the score, not the reason behind it.
Children and teens use a different scale. Their score is read against age and sex percentiles instead of fixed bands. A growth chart tracks the trend over months and years. Ask a paediatrician to read any child result before you draw a conclusion.
Limits of BMI
BMI misses a few things by design. It cannot split fat from muscle and says nothing about where fat sits on your body. It fits average adults better than athletes or older people who have lost muscle. Treat the score as one signal and pair it with other checks for a full picture.
How to Improve Your Score
Moving your score toward the healthy band rarely needs a drastic plan. Steady changes to food and daily activity carry most of the load, and a brisk walk on most days lifts your baseline over weeks. Check your BMI every few weeks and watch small wins add up. Speak with a doctor before any big shift in diet or exercise.
Sources and Review
The ranges on this page come from public health sources. The World Health Organization defines overweight as a BMI of 25 or more and obesity as 30 or more in adults. The CDC lists the adult categories of underweight, healthy weight, overweight and obesity. You can read both originals here: WHO fact sheet on obesity and overweight and CDC adult BMI categories.
The CalculatorsSpot team last checked the formula and the ranges against these sources in October 2026. You can read who we are and how we test our tools on the About page. This page gives general information and is not medical advice, so ask a doctor to read your result in context.
Frequently asked questions
How does a BMI calculator work?
It divides your weight by your height squared and matches the score to a standard band.
What is a healthy body mass index range?
For most adults a score of 18.5 to 24.9 counts as healthy.
Does BMI account for muscle mass?
No. It cannot separate fat from muscle, so a very muscular person can score high without carrying excess fat.
Is BMI different for children?
Yes. Children and teens are read against age and sex percentiles rather than the fixed adult bands.
Is this BMI calculator free?
Yes, it runs in your browser with no sign up and stores nothing.
Related calculators
Other tools people use alongside the BMI calculator.