BMI Calculator: Check Your Body Mass Index
Body mass index (BMI) is the quickest way to see whether your weight sits in a healthy range for your height. This free calculator works in metric and imperial units — enter your height and weight, and it instantly returns your BMI score, your weight category, and the healthy weight range you should aim for. It uses the same classification doctors and dietitians use worldwide.
BMI Calculator
How to Use This Calculator
Choose your units first — Metric (kg & cm) or Imperial (lbs & ft/in). The calculator shows the right fields automatically, and it converts the values you have entered when you switch, so you never have to redo anything.
Enter your current weight and your height. If you are not sure of your exact height, stand against a wall, mark the top of your head, and measure from the floor. Weigh yourself in the morning before breakfast for the most consistent number.
Click Calculate and the tool shows your BMI score, your weight category (underweight, normal weight, overweight or obese), and the healthy weight range for your height. Click Reset to clear everything and start over.
The Formula
BMI is your weight in kilograms divided by your height in meters squared: BMI = weight (kg) ÷ height (m)². For imperial measurements the calculator converts pounds to kilograms and feet and inches to meters first, then applies the same formula — both unit systems give the same score.
The World Health Organization groups adult scores into four categories: 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. Obesity is further split into class I (30–34.9), class II (35–39.9) and class III (40+).
Worked example: a 70 kg person who is 170 cm (1.70 m) tall has a BMI of 70 ÷ 1.70² = 70 ÷ 2.89 = 24.2, which lands in the Normal weight range. The healthy weight range for that height is 18.5 × 2.89 = 53.5 kg at the low end up to 24.9 × 2.89 = 72.0 kg at the high end — about 118 to 159 lbs.
Tips
Judge your BMI by the trend, not by a single reading. Weigh yourself at the same time of day, once a week, and compare over months — a slow, steady move toward the middle of the healthy range is worth far more than a perfect number on one random Tuesday.
Remember that BMI is a screening tool, not a diagnosis. If you are athletic or carry a lot of muscle, your BMI can look high while your body fat is perfectly healthy — in that case a body fat measurement tells you more.
If your BMI is outside the healthy range, aim for the healthy weight range shown in your results as a long-term target. Small, sustainable changes — a modest calorie deficit, more protein and vegetables, and a couple of strength sessions a week — move the number faster than crash diets, and they stick.
Frequently Asked Questions
What is BMI and what does it measure?
Body mass index is a number calculated from your height and weight — your weight in kilograms divided by your height in meters squared. It estimates whether your weight is proportionate to your height, which is why doctors and researchers use it as a quick screening tool for underweight, overweight and obesity in adults.
Is BMI accurate for athletes or muscular people?
Not always. BMI does not distinguish muscle from fat, so very muscular people — athletes, bodybuilders and weightlifters — can score as "overweight" or "obese" while carrying very little body fat. If you train with weights regularly, a body fat measurement such as the U.S. Navy method is a more useful number.
What is a healthy BMI range for adults?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy range. Scores below 18.5 are underweight, 25 to 29.9 are overweight, and 30 or above are obese. These ranges apply to most adults aged 18 and older; children and teens need age-specific charts instead.
Does BMI apply to children and teens?
Not in the same way. For ages 2 to 19, BMI is compared with percentile charts for the child's age and sex, because body composition changes rapidly during growth. A pediatrician or family doctor should interpret a child's BMI rather than the adult categories.
How can I lower my BMI?
Lowering your BMI means losing body weight, which takes a modest daily calorie deficit — roughly 300 to 500 calories. Prioritize protein and vegetables, add strength training so you keep muscle while losing fat, and aim to lose about 1 to 2 pounds (0.5 to 1 kg) per week. Our calorie and TDEE calculators can help you find the right daily target.