BMI Calculator
Find your body mass index in one step. Type your height and weight, switch between metric and imperial, and see your category plus the healthy weight range for your height.
Enter your height and weight, then press Calculate to see your result.
How to use the BMI calculator
Choose your units
Tap Metric for centimetres and kilograms, or Imperial for feet, inches and pounds. Your entries convert automatically.
Enter height and weight
Use your most recent measurements. Morning, before breakfast, gives the most consistent reading if you track over time.
Read your result
You get your BMI number, the category it falls in, and the weight range that would put you in the healthy band for your height.
What the number means
A quick screening tool
BMI compares your weight to your height and sorts adults into broad bands. It is a fast, cheap first check that health services worldwide use to flag when weight might be worth a closer look.
Nothing leaves your browser
Every calculation happens on your own device with plain JavaScript. No height, no weight and no result is ever sent anywhere, so you can check as often as you like in complete privacy.
Know its limits
BMI does not separate muscle from fat or account for where weight sits. A lean athlete can score high; an older adult with low muscle can score low. Treat it as one clue, not a verdict.
Understanding body mass index
Body mass index is your weight in kilograms divided by the square of your height in metres. That single ratio has been used since the 19th century as a rough way to describe body size across a population, and it remains popular because it needs only two measurements anyone can take at home.
The standard adult categories
The World Health Organization groups adult BMI into four main bands. They apply to men and women aged 20 and over and are the same numbers used by most clinics.
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25.0 to 29.9 |
| Obesity | 30.0 and above |
Why height matters so much
Because BMI divides by height squared, a few centimetres change the healthy weight window more than most people expect. Someone 1.60 m tall sits in the healthy band between roughly 47 and 64 kg, while someone 1.85 m tall has a healthy band of about 63 to 85 kg. The calculator works this range out for you so you can see exactly where you stand.
When BMI can mislead
The formula treats every kilogram the same, whether it is muscle, bone or fat. Bodybuilders and heavy-training athletes often land in the overweight or obese bands despite low body fat. Pregnancy, a growing child, and older adults who have lost muscle are other cases where the plain number needs context. For a fuller picture, pair it with a body fat estimate and a waist measurement.
Children and teenagers
For anyone under 20, BMI is read against age-and-sex percentile charts rather than the fixed adult bands, because healthy body composition changes rapidly during growth. This tool is designed for adults; use a paediatric BMI-for-age chart for younger ages.
Frequently asked questions
Is my data sent to a server?
No. The calculator runs entirely in your browser with JavaScript. Your height, weight and result never leave your device and nothing is stored after you close the tab.
How is BMI calculated?
In metric it is weight in kilograms divided by height in metres squared. In imperial the tool converts your feet, inches and pounds to metric first, so both unit systems give the same result.
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is classed as healthy. Below that is underweight, 25 to 29.9 is overweight, and 30 or higher is in the obesity range.
Does BMI work for athletes?
Not well. Muscle is denser than fat, so very muscular people often read as overweight even at low body fat. If you train hard, check your body fat percentage alongside BMI for a clearer view.
Is BMI the same for men and women?
The adult bands are the same for both. Women naturally carry more body fat at a given BMI, so consider it a general guide rather than a precise body-fat reading.
Can I use it for my child?
This tool uses the fixed adult bands, which are not valid for anyone under 20. Children and teens should be assessed with BMI-for-age percentile charts instead.