BMI And BMR Calculators is a BMR and BMI measurement tool. Use different measurements units (Support Metric and Imperial units). Save and track results. Calculate your BMR with 3 different estimation formulas: The Original Harris-Benedict Equation, The Revised Harris-Benedict Equation, The Mifflin St Jeor Equation. Body Mass Index(BMI) is used to estimate your total amount of fat. It is only an approximate measure of the best weight for your health. Basal metabolic rate (BMR) refers to the minimum amount of energy -- in the form of calories -- that your body requires to complete its normal functions, such as breathing, breaking down food, and keeping your heart and brain working. Age, gender, weight, and physical activity directly effect on basal metabolic rate.