How to Calculate Your BMI (Free Calculator + What It Means)
Body Mass Index (BMI) is a simple number that relates your weight to your height, used as a quick screening tool for whether you're in a healthy weight range. It's easy to calculate and useful as a starting point — but it's also widely misunderstood. This guide shows how to calculate your BMI for free, what the categories mean, and, just as importantly, what BMI can't tell you.
⚖️ Try the BMI Calculator now — freeOpen →BMI gives you a fast, standardized snapshot that's used by health services worldwide as an initial screen. Knowing your BMI — and understanding its limits — helps you have a more informed conversation about your health, without over-relying on a single number.
The formula and the categories
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). For example, 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) = 22.9. In imperial units it's weight in pounds ÷ height in inches², multiplied by 703.
The standard adult categories are: under 18.5 is underweight, 18.5–24.9 is a healthy weight, 25–29.9 is overweight, and 30 or above is in the obese range. The calculator does the math and shows your category instantly.
What BMI can't tell you
BMI is a screening tool, not a diagnosis, and it has real blind spots. It doesn't distinguish muscle from fat, so very muscular people (athletes) can score "overweight" while being extremely fit. It also doesn't account for where fat is stored, age, sex, or ethnicity, all of which affect health.
Treat BMI as one data point among many. Waist measurement, activity level, diet, and blood markers give a fuller picture. For any health decision, talk to a healthcare professional rather than relying on BMI alone.
Step-by-step
Common mistakes to avoid
Pro tips
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared (kg/m²). In imperial: pounds ÷ inches² × 703.
What is a healthy BMI?
For adults, a BMI between 18.5 and 24.9 is generally considered a healthy weight range.
Is BMI accurate for everyone?
No — it doesn't distinguish muscle from fat and ignores age, sex and body composition, so it's a screening tool, not a diagnosis.
Is the calculator free and private?
Yes — free with no sign-up, and it runs in your browser, so your details aren't uploaded.
Can I use BMI for children?
Adult categories don't apply to children, who are assessed with age- and sex-specific percentile charts.
BMI is a quick, useful screening number — as long as you know its limits. Calculate it in seconds, note your category, but read it alongside other measures and professional advice rather than as a verdict. Free and private, in your browser.