BMI and body fat percentage both estimate body size, but they answer different questions. BMI compares weight with height. Body fat percentage estimates how much of your weight is fat mass.
Start with the BMI Calculator for a quick screening number. Then use the Body Fat Calculator for a more detailed estimate based on body measurements.
What BMI does well
BMI is fast and easy. It can help identify broad weight categories for adults. It is commonly used in the United States and Canada because it only requires height and weight.
Where BMI falls short
BMI does not measure muscle, bone density, body shape, or fat distribution. A muscular person may have a high BMI without having high body fat.
When body fat percentage helps
Body fat percentage can be more useful for fitness goals. It still has limits, but it gives a better estimate of body composition than BMI alone.
You can also compare results with the Ideal Weight Calculator and Calorie Calculator for broader planning.