Ask the Experts: How Many Calories Should I Eat?

Want to figure out how many calories you need to eat each day? Learn the factors involved and how to do the calculation.

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Q: How many calories should I eat?

A: Every person needs a different amount of calories each day, so we cannot recommend a single number. However, you can get an idea of how many calories you need from a simple math equation.

If you aren't familiar, a calorie is a unit of energy. Food with more calories delivers more energy, which can be converted into adenosine triphosphate (ATP) and used by the body as a source of fuel.

Determine the number of calories you need by using four factors.

  1. Resting Metabolic Rate – The amount of calories your body burns when you lie motionless.
  2. Activity – Every time you move, you burn energy, so you have to factor in your level of activity.
  3. Heating effect of food – Food naturally heats your body and causes increased energy expenditure. The effect is negligible, and for purpose of this article, we will ignore this factor.
  4. Your goal – The amount of calories you eat depends heavily on whether you are trying to lose or maintain weight, build muscle or achieve other goals

The only precisely accurate way to determine the number of calories you need is with scientific equipment. However, the following equation will help you get a pretty accurate estimate.


  • Weight in lbs./2.2 = Weight in kg
  • [% Body Fat* /100] x Weight in kg = Body Fat in kg
  • Weight in kg – Body Fat in kg = Lean Body Mass
  • 500 + [22 x Lean Body Mass] = Resting Metabolic Rate

* Percent of body fat can be estimated by many bathroom scales or through a test at a local fitness facility.

Activity Level Chart

Calorie equation  


Resting Metabolic Rate x Estimated Activity = Calories Required Per Day

Remember that if you are trying to lose or gain weight, you need to adjust the amount of calories accordingly. A general recommendation is to trim or add 500 calories off his estimate to achieve your desired goal.


  • A 176-pound athlete weighs 80 kg
  • His percentage of body fat is 12%
  • [12/100] x 80 = 9.6 kg of body fat
  • Weight in kg (80) minus body fat in kg (9.6) = 70.4 kg of lean body mass
  • 500 + [22 x 70.4] = resting metabolic rate of 2048.8
  • Our athlete trains daily, so we will use the activity range of 1.6 to 2.0
  • 2048.8 x 1.6 = 3,278 calories per day; 2048.8 x 2.0 = 4,098 calories per day
  • If the athlete is trying to gain weight, he would use the higher end of the range and maybe even bump it up by 500 calories.

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