Check your Body Mass Index instantly.
Body Mass Index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters (kg/m²) — a simple formula developed in the 1830s that's still the most widely used screening tool for weight categories today. This calculator does that math for you instantly, accepting either metric (kg, cm) or imperial (lb, ft/in) input and converting automatically, so you get an accurate result regardless of which unit system you're used to.
The World Health Organization defines four standard categories: below 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 and above is obese. These ranges apply to most adults, though they were developed primarily using data from European populations, and several health organizations now recommend slightly lower cutoffs for South and East Asian populations, where health risks appear at somewhat lower BMI values.
BMI doesn't distinguish between muscle and fat mass, which means a muscular athlete can register as 'overweight' or even 'obese' despite having very low body fat — this is BMI's most commonly cited weakness. It also doesn't account for where fat is distributed on the body, age-related muscle loss, or bone density differences between individuals. For a more complete picture, pair this BMI result with our Body Fat Percentage Calculator, which measures body composition directly rather than inferring it from height and weight alone.
A single BMI reading is a starting point for a conversation with a doctor, not a final health verdict on its own — two people with identical BMI can have very different health profiles depending on muscle mass, fat distribution, and overall fitness. If your result falls outside the normal range, the most useful next step is discussing it alongside other measures — waist circumference, body fat percentage, blood pressure, and activity level — with a healthcare provider, rather than reacting to the BMI number in isolation.
For most adults, 18.5 to 24.9 is considered the normal, healthy weight range according to WHO standards.
Not always — BMI can't distinguish muscle from fat, so athletes with high muscle mass often register as overweight despite low body fat. A body fat percentage measurement is more accurate for this group.
BMI equals your weight in kilograms divided by your height in meters squared (kg/m²).
No — children and teens require age- and sex-specific BMI percentile charts rather than the fixed adult categories used here.
BMI estimates weight status from height and weight only, while body fat percentage measures the actual proportion of fat versus lean mass in your body — a more direct composition measure.