BMI Calculator
Enter height and weight to see a general adult BMI category.
BMI
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BMI Calculator
Calculate body mass index with metric or US inputs.
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How To Use The BMI Calculator
Pick Metric to enter your height in centimetres and weight in kilograms, or US to enter height in feet and inches with weight in pounds. As soon as both fields hold valid numbers, the large BMI readout updates and the strip below shows your WHO weight Category together with a short note. Nothing is submitted and there is no button to press: the value recalculates live as you type, so you can try different weights or heights and watch the category change instantly.
What Body Mass Index Actually Measures
Body Mass Index is a single number that relates your weight to your height. The metric formula is weight in kilograms divided by your height in metres squared, written as kg / m². A person who is 1.75 m tall and weighs 70 kg has a BMI of 70 / (1.75 × 1.75) = 22.9. Because tall people are naturally heavier, dividing by height squared makes the figure roughly comparable across different statures. BMI is a screening proxy for body fat at the population level, but it measures total mass, not fat specifically, which is why context always matters when you read the result.
WHO Adult BMI Categories
The World Health Organization sorts adult BMI into four broad bands. Find the row that contains your number to see the category name and what it generally indicates.
| BMI range | Category | General interpretation |
|---|---|---|
Below 18.5 | Underweight | Body mass is low relative to height |
18.5 - 24.9 | Normal weight | Mass falls in the typical reference band |
25.0 - 29.9 | Overweight | Mass is above the reference band |
30.0 and above | Obese | Mass is well above the reference band |
These bands apply only to adults aged 20 and over and are the same regardless of sex. They do not adjust for muscle, age, or ethnicity.
Worked Example And Imperial Units
Suppose you are 5 ft 9 in tall and weigh 154 lb. The imperial formula is pounds divided by height in inches squared, multiplied by 703: that is 154 / (69 × 69) × 703 = 22.7, which sits in the normal range. The calculator converts your feet, inches, and pounds to metric behind the scenes, so the US and metric tabs always return the same BMI for the same body. The 703 factor is simply the constant that lets pounds and inches reproduce the original kg / m² value.
Why This Tool Is Useful
BMI is a fast, widely understood first checkpoint for thinking about weight relative to height. It needs only two measurements you can take at home, costs nothing, and gives a number you can track over months to spot a trend. Doctors, insurers, and public-health bodies all use the same bands, so the figure this calculator produces lines up with the one used in clinics and research. It is a useful conversation starter, not a verdict, and works best alongside other signals such as how you feel, your activity level, and your waist measurement. This is an estimate, not professional medical advice.
Accuracy And Privacy
Everything is calculated locally in your browser using JavaScript. Your height and weight are never sent to a server, stored, or shared with anyone, so you can use the tool with complete confidence. Keep in mind that BMI does not distinguish muscle from fat, ignores where fat is stored, and is not valid for children, pregnant people, or elite athletes. Read the result as a rough screening band and consult a qualified healthcare professional before drawing any conclusions about your health.
FAQ
What is a healthy BMI range for adults?
Using the WHO adult categories, a BMI from 18.5 to 24.9 is classified as the normal weight range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. These thresholds are general screening bands rather than personal targets, and they apply only to adults aged 20 and over.
Why is BMI inaccurate for athletes and very muscular people?
BMI only compares weight to height and cannot tell muscle from fat. Muscle is denser than fat, so a lean, heavily trained athlete can land in the overweight or even obese band despite carrying very little body fat. For people with high muscle mass, measures such as body fat percentage, waist circumference, or waist-to-height ratio give a far more meaningful picture.
Can I use this BMI calculator for children?
No. This calculator uses the adult WHO categories, which do not apply to anyone under 20. Children and teenagers are assessed with age- and sex-specific BMI-for-age percentile charts, because healthy body composition changes a great deal during growth. For a child or teen, ask a pediatrician or use an official growth percentile tool instead.
What is the difference between metric and imperial BMI?
There is no difference in the final number. The metric formula divides weight in kilograms by height in metres squared. The imperial formula multiplies pounds divided by inches squared by 703, which is just a unit-conversion factor. This calculator converts feet, inches, and pounds to metric internally, so both unit systems give the same BMI for the same body.
Is BMI medical advice?
No. BMI is a general population screening estimate, not a diagnosis or a measure of individual health. It does not account for age, sex, ethnicity, muscle mass, bone density, or fat distribution. Treat the result as a rough starting point and talk to a qualified healthcare professional before making any decision about your weight or health.