A BMI calculator (Body Mass Index calculator) is an online health tool used to measure whether a person has a healthy body weight according to their height and weight. It calculates BMI by dividing a person’s weight in kilograms by the square of their height in meters. Based on the result, it classifies the person into categories such as underweight, normal weight, overweight, or obese. This tool is widely used by individuals, fitness trainers, and healthcare professionals to quickly assess body fitness and health status. A BMI calculator is simple to use—users just enter their height and weight, and it instantly shows the result. Overall, it is a useful and convenient tool for understanding basic health and fitness levels.