BMI Calculator
How it works
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). We classify the result using the World Health Organization bands: underweight below 18.5, normal 18.5–24.9, overweight 25–29.9, and obesity classes I–III from 30 upward.
BMI doesn’t distinguish muscle from fat, so very muscular people can read as “overweight” despite low body fat. Treat it as a starting point, not a diagnosis.
Frequently asked questions
What is a healthy BMI?+
The World Health Organization considers a BMI of 18.5 to 24.9 a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above falls into the obesity classes.
How is BMI calculated?+
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). In imperial units it's 703 × weight in pounds ÷ height in inches squared. This calculator handles the conversion for you.
Is BMI accurate for athletes and muscular people?+
Not always. BMI can't tell muscle from fat, so very muscular people often read as 'overweight' despite low body fat. Use it as a quick screen, and pair it with a body-fat estimate or waist measurement for a fuller picture.
What's the difference between BMI and body fat percentage?+
BMI is a ratio of weight to height and ignores body composition. Body fat percentage measures how much of your weight is actually fat. Two people with the same BMI can have very different body-fat levels.
How can I lower my BMI?+
Since BMI is driven by weight and height, lowering it means losing body weight — through a modest calorie deficit and more activity. Flun makes the calorie side automatic by logging your meals for you.