BMI Calculator
Calculate your body mass index (BMI) from your height and weight. BMI is a quick screening tool that sorts weight into categories, a useful starting point, though not the whole picture.
How the BMI calculator works
Body mass index is your weight in kilograms divided by the square of your height in metres. It gives a single number that estimates whether your weight sits in a healthy range for your height.
BMI categories
For adults, the standard ranges are: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or above is obese. These come from the World Health Organization and apply to most adults aged 20 and over.
What BMI does not tell you
BMI does not distinguish muscle from fat or show where you carry weight, so very muscular people can read as overweight while the number can miss excess fat in others. Treat it as one simple signal among many, not a diagnosis, waist size, body composition, and overall health matter too.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. These are screening ranges, not a diagnosis.
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). In imperial units it is weight in pounds times 703, divided by height in inches squared. This calculator does the conversion for you in either unit system.
Is BMI accurate?
BMI is a useful, quick screening tool, but it has real limits for individuals. It cannot tell muscle from fat, so athletes may score high despite low body fat, and it can understate fat in others. Use it alongside other measures like waist circumference.
Does BMI work for everyone?
The standard categories apply to most adults aged 20 and over. They are not designed for children and teens (who use age- and sex-specific charts), and they can be less accurate for pregnant people, older adults, and some ethnic groups. When in doubt, ask a healthcare professional.
What should I do if my BMI is outside the healthy range?
A BMI outside the healthy range is a prompt to look closer, not a verdict. If you want to change it, small, sustainable habits, a modest calorie adjustment, more protein, and regular movement, work better than crash diets. A doctor or dietitian can help you set a safe, personal plan.