How to Figure Out Your BMI & Caloric Needs

Your BMI can indicate if you need to lose or gain weight.

Creatas Images/Creatas/Getty Images

Calculating your body mass index, or BMI, can help you figure out if you weigh too little, too much, or just the right amount, based on your height and weight. According to the National Heart, Lung, and Blood Institute and, a BMI of between 18.5 and 24.9 indicates you are at a normal weight. A BMI that is too high (above 24.9) or too low (below 18.5) can indicate that you need to lose or gain weight. To do so, you should first determine how many calories your body requires to maintain its current activity level, and then adjust up or down depending on your weight goals.

How to figure out your BMI


Weigh yourself and measure your height in inches.


Square your height in inches - that is, multiply your height by itself. For example, if you are 5'8”, or 68 inches, multiply 68 by 68, which comes to 4,624.


Divide your weight in pounds by the result of squaring your height in inches. For example, if you weigh 170 pounds, divide 170 by 4,624, which results in 0.0368.


Multiply the quotient by 703. For example, multiply 0.0368 by 703, which, rounded to the nearest tenth, results in 25.87, That result would land squarely in the overweight range, according to the National Heart, Lung, and Blood Institute.

How to figure out your caloric needs


Calculate your caloric needs using an online calculator, such as the one that provides.


Enter your age, height, weight and gender.


Select your activity level -- Inactive, somewhat active, active, and very active. Because the number of calories you need depends on how active you are (which is how much energy you expend), select the activity level that best describes how active you are each day. Your daily calorie needs will change based on how active or inactive you are.


Use the calorie calculator as often as you want, especially if your activity level changes, to ensure you are consuming the optimal number of calories for your activity level. This will be the optimal number of calories to help you reach your weight-loss or weight-gain goals.


  • Before beginning any weight-loss program, check with your doctor.
  • You can use an online BMI calculator, such as what the Mayo Clinic and the National Heart, Lung, and Blood Institute provides.
  • To calculate your caloric needs without using an online calculator, you can use the Harris-Benedict Formula, which first calculates your base metabolic rate (BMR) and then factors in how active you are to estimate how many calories you need to maintain your present weight. The American Council on Exercise and Health FIT provides information about using the formula and interpreting the results.


  • The BMI cannot distinguish between how much of your weight is fat and how much is muscle. Because muscle weighs more than fat, the BMI may overestimate body fat in athletes, bodybuilders and others with muscular builds. It can also underestimate body fat in people with less-muscular builds or the elderly, who may have lost muscle as they've aged. You may want to perform other health assessments, such as the skinfold test, or the waist circumference test, to better estimate if you are overweight or underweight.