The amount of protein, carbohydrates, and fat you need to eat — the macronutrients in your diet, or macros — should be easy to figure out. However, the equations used to determine the number of grams are often confusing. This is especially true for protein because the equations are so similar. It’s imperative that you know the correct calculations lest you get too much or too little protein, which could derail your overall health.

Why You Need a Specific Amount

Protein is essential for a number of body functions including, among others:

  • Metabolism regulation
  • Acid/base balance regulation
  • Muscle growth and maintenance
  • Tissue repair and maintenance

Getting too little protein means your body won’t have the compounds it needs to handle all of these functions properly. You may find it harder to build muscle, for example. Getting too much protein can lead to constipation, dehydration, weight gain, potentially higher risks for high cholesterol and diseases like cancer, and even kidney problems.

The correct amount of protein you need falls in a range, so it’s relatively easy to have variety in your diet without setting off symptoms of over- or under-intake of protein.

The Potential Formulas

Calculating daily protein needs requires a formula. Two rely solely on body weight, while one requires you to know your body fat percentage, and thus your lean body mass percentage (which is just 100 percent minus your body fat percentage).

The two that require only body weight are the easiest to calculate but also the easiest to confuse because they are essentially the same, but one relies on pounds and the other on kilograms. The basic formulas are also meant for sedentary people:

  • 0.8 x (your weight in kilograms)
  • 0.36 x (your weight in pounds)

As your activity levels increase, so does your need for protein. For example, a competitive athlete would use between 0.54 and 0.82 to determine the number of protein grams needed daily.

Once you know your general activity level, using a body-weight-based formula gives you the best estimate per current thinking. Diet advice changes constantly, and you’ll find many who believe people already eat way too much or way too little protein. With the two body-weight formulas, though, you’ll get a moderate number that you can then tweak depending on how you feel.

The formula that requires lean body mass and body-fat percentage is more difficult to use; the calculation isn’t hard, but it’s comparatively vague because if you don’t have an official body-fat measurement, you’re pretty much guessing.

In general, it’s lean body mass percentage in pounds multiplied by a factor based on activity level. You’ll find variations from 0.5 for sedentary people to 0.9 to 1.0 for very active people and athletes. For example, a sedentary person weighing 200 pounds with a body-fat percentage of 45 percent has a lean body mass percentage of 55 percent. 200 x 0.55 = 110; that person would then multiply 110 by 0.5 to get a value of 55 grams of protein per day. However, if the body-fat percentage is an estimate based on a visual guess, for example, the entire calculation could be wildly off.

To start, use the body-weight-based formulas and keep the units and factors straight. See how getting that much protein makes you feel after a while, and recalculate as your activity level changes.