BMI Calculator
Free BMI Calculator to enter your weight and height and instantly calculate your Body Mass Index and see your WHO weight category.
Result
| Your BMI | ||
|---|---|---|
| Category |
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The BMI Calculator instantly works out your Body Mass Index from your weight and height, and shows which standard weight category you fall into. Enter your weight in kilograms and height in centimeters, click calculate, and get your result in a second. Free, private, and runs entirely in your browser.
What BMI Tells You
Body Mass Index is a simple, widely-used screening number that relates your weight to your height. It gives a quick sense of whether your weight sits in a healthy range for your height, which is why doctors, gyms, and health services use it as a fast first check. This calculator does the maths for you and places your result in the standard category.
How to Use It
- Enter your weight in kilograms.
- Enter your height in centimeters.
- Calculate to see your BMI and category.
The Formula
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). The tool converts your height from centimeters to metres for you. For example, 70 kg at 175 cm gives 70 / (1.75 × 1.75) = 22.9, which falls in the normal range.
BMI Categories (WHO, adults)
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obese |
An Honest Note on What BMI Can and Can't Do
BMI is genuinely useful as a quick screen, but it's important to be honest about its limits. Because it uses only height and weight, it can't distinguish muscle from fat — a very muscular athlete may register as "overweight" despite low body fat, while someone with little muscle may carry excess fat at a "normal" BMI. It also doesn't directly account for age, sex, ethnicity, or where fat is stored. Treat your result as a starting point, not a diagnosis.
When to Seek Professional Advice
If your BMI falls outside the normal range and you're concerned, the best step is to talk with a doctor or qualified healthcare professional. They can look at your full picture — body composition, activity levels, family history, and more — which BMI alone can't capture. For children and teens, age-and-sex-specific charts are used instead of the adult categories.
Free and Private
The whole calculation runs in your browser, so your weight and height are never sent anywhere or stored. Use it as often as you like, free and with no signup.
BMI Calculator FAQs
How do I calculate my BMI?
Enter your weight in kilograms and your height in centimeters, then click Calculate. The tool divides your weight by your height in meters squared to produce your Body Mass Index, and shows the standard category your result falls into. It's instant, free, and runs entirely in your browser.
What is the BMI formula?
BMI equals your weight in kilograms divided by your height in metres squared (kg/m²). For example, a person weighing 70 kg at 1.75 m tall has a BMI of 70 / (1.75 × 1.75) = 22.9. This calculator does the maths for you, including converting your height from centimeters to metres.
What are the BMI categories?
The World Health Organization uses four standard bands for adults: a BMI below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obese. The calculator tells you which band your result falls into so you can see where you stand at a glance.
Is BMI an accurate measure of health?
BMI is a useful, quick screening tool, but it has real limits and isn't a complete picture of health. Because it only uses height and weight, it can't tell muscle from fat — so very muscular people may read as overweight despite low body fat, while others may carry excess fat at a normal BMI. Treat it as a starting point, not a diagnosis, and consult a healthcare professional for a full assessment.
Does BMI work the same for everyone?
Not perfectly. Standard BMI categories were developed mainly for adults and don't account for age, sex, ethnicity, or athletic build in the basic formula. Children and teens use age-and-sex-specific percentiles instead, and some populations have different risk thresholds. For most adults it's a reasonable general guide, but individual interpretation benefits from professional context.
Why does the calculator ask for centimeters?
Because most people know their height in centimeters, the tool accepts cm and converts it to metres for the formula automatically (dividing by 100). This keeps it simple — just enter your height as you normally would, for example 175, and the calculator handles the rest.
Is my data private?
Yes. The entire calculation happens in your browser, so your weight and height are never sent to a server or stored. You can use it as often as you like, completely privately and free, with no signup required.
What should I do with my BMI result?
Use it as one piece of information among many. If your result sits outside the normal range and you're concerned, the best next step is to speak with a doctor or qualified healthcare professional, who can consider your full picture — including body composition, activity, and medical history — rather than BMI alone.