BMI Calculator (Body Mass Index)
Body mass index (BMI) is your weight (kg) divided by the square of your height (m²). For example, someone who is 1.70 m tall and weighs 70.5 kg has a BMI of 24.4. Enter your height and weight — your value, category and the healthy weight range for your height are calculated instantly.
Enter your height and weight — your result appears here instantly.
BMI does not distinguish muscle from fat; read your result together with waist circumference and your overall health.
Your inputs never leave your device; the calculation runs in your browser and nothing is sent to a server.
What do the BMI ranges mean?
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity (Class 1) |
| 35.0 – 39.9 | Obesity (Class 2) |
| 40.0 and above | Obesity (Class 3) |
These are the general adult categories defined by the World Health Organization; a personal assessment varies with age, muscle mass and health status.
For informational purposes only; not medical advice. BMI is a screening tool and does not diagnose. Consult a doctor or dietitian for an assessment.
Body mass index is the most widely used screening measure for a quick sense of whether your weight is in balance with your height. The math is simple: your weight in kilograms is divided by the square of your height in meters. Of two people at the same weight, the shorter one has the higher BMI, because the same mass is spread over a smaller frame.
The most practical way to read the result is to see which range the number falls into. For adults, 18.5–24.9 is considered normal; this calculator converts that range into your height and shows the corresponding healthy weight range too. For someone 1.70 m tall, for example, that range is roughly 53.5–72.0 kg.
What BMI Measures — and What It Can't
BMI uses only height and weight; it cannot tell whether your body is made of muscle or fat. Someone who lifts weights regularly can land in the "overweight" range while carrying very little body fat. Conversely, a person who has lost muscle can show a normal-looking BMI that hides a high fat percentage. That is why BMI is a starting point; it becomes meaningful alongside waist circumference, body composition and your overall health picture.
Toward the Healthy Range: Calorie Balance
Whichever direction you want to move your BMI, the mechanism is the same: calorie balance. Taking in less than you burn leads to gradual weight loss; more leads to gain. The first step is to calculate your daily calorie needs; the second is to track what you eat consistently. Rather than trying to change the number fast, progressing with a small, sustainable difference protects muscle and makes the habit stick.
An important note: the ranges on this page are for adults. During pregnancy, under age 18, and with chronic conditions, BMI is assessed differently — talk to a health professional before making a plan.
Frequently asked
How is body mass index calculated?
Body mass index is your weight in kilograms divided by the square of your height in meters: BMI = kg / m². For example, someone who is 1.70 m tall and weighs 70.5 kg has a BMI of 70.5 ÷ (1.70 × 1.70) = 24.4. The result is then classified using the World Health Organization's adult ranges.
What is a healthy BMI range?
For adults, a BMI between 18.5 and 24.9 is considered normal. Below 18.5 is underweight, 25.0-29.9 is overweight, and 30 or above is classified as obese. These ranges are general; age, muscle mass and body build mean a personal assessment should be made with a health professional.
What are the limitations of BMI?
BMI uses only height and weight, so it cannot tell muscle from fat. A muscular athlete can have a high BMI while being perfectly healthy, and in older adults a normal-looking BMI can hide a high body-fat percentage caused by muscle loss. That is why BMI is a screening tool, not a diagnosis, and is best read together with waist circumference and body composition.
Is BMI used during pregnancy or for children?
The calculation on this page is for adults. During pregnancy, BMI is tracked differently and under medical supervision. For children and teenagers, BMI is assessed with age- and sex-specific percentile charts rather than a single range. In both cases the right person to consult is a doctor or dietitian.
Why does waist circumference matter?
Fat stored around the abdomen is linked to metabolic risk more directly than BMI alone. Two people can have the same BMI but very different waist measurements. That is why health organizations recommend reading BMI alongside waist circumference.
What should I do to move my BMI into the healthy range?
Weight change comes down to calorie balance: taking in less than you burn leads to weight loss, and more leads to gain. The first step is to learn your daily calorie needs, then track what you eat consistently. In cases of chronic illness, pregnancy or a very high or low BMI, the plan should be set with a doctor or dietitian.
You know your number — now build the balance.
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