How Calories Are Measured

By Ashley Henshaw. May 7th 2016

Dieters are often hyperaware of how many calories they consume each day. We all know that calories play a role in weight gain or loss, but what exactly is a calorie? How are calories measured? These questions and more will be answered in this article.

What Are Calories, Anyway?

Calories are units used to measure energy. But 1 calorie on a nutrition label actually indicates 1 kilocalorie (kcal), which is 1,000 calories. Basically, 1 kcal (or 1 calorie as found on a nutrition label) is how much energy, or heat, is needed to raise the temperature of 1 gram of water by 1 degree Celsius. This way of measuring energy applies to more than just food. In fact, a gallon of gasoline contains about 31,000,000 calories.

Calories can also tell you a little something about what components a food contains. For instance, a gram of fat contains 9 calories, while a gram of carbohydrates contains 4 calories. That’s what it means when a nutrition label lists the “calories from fat” in addition to “calories.”

So how does this relate to the way calories affect our bodies? Basically, calories provide our body with energy. We “burn” the calories through metabolic processes that breakdown the different parts of the food we eat. The molecules that result from these processes are either used up immediately or are sent to react with oxygen to release stored energy. When you eat too many calories per day, you gain weight because your body isn’t using up that much energy.

Calorie Measurement Methods

When calories were first measured, it was done by literally burning the food to see how much energy it produced. Food was placed inside a sealed container called bomb calorimeter. Water surrounded the container, and when the food was burned the rise in water temperature was measured in order to count the calories.

The calorie measurement methods use today, however, are quite different. In most cases, food components are used to determine a food’s calorie content. This USDA-regulated practice, which is called the Atwater system, is based on indirect calorie estimations. The energy-containing nutrients found in food – proteins, carbohydrates, fats and alcohol are counted up and then the calories designated to each of these components are combined to give the food’s total calorie count. Food companies can access a database of this information to help determine their products’ calorie information.

Even though the USDA’s published database offers estimates on calories for thousands of foods, some food companies utilize labs with highly sophisticated, modern calorimeters to make sure their calorie counts are correct.

Calorie Labeling Regulations

The FDA requires that all food companies print accurate calorie data on nutrition labels for every product. This practice makes it clear to consumers how many calories they are consuming per serving. However, it doesn’t say which method they must use to collect this data, so the company might use a lab or they may just refer to the USDA’s published estimates.

The FDA also requires information about how many calories come from fat. This helps individuals who are looking to monitor their intake of fats as well as calories.

General Calorie Guidelines

The average person should consume about 2,000 calories per day. This number may be slightly high or low for certain people based on their individual health needs. However, most people generally regard 2,000 as the average amount of calories needed per day.

In addition to this daily guideline, there is also a general guideline for how many calories are in a serving. According to the FDA, the following rules apply on a per-serving basis:

  • 40 calories is low
  • 100 calories is moderate
  • 400 calories or more is high


One of the key mistakes that many people make in looking at calorie intake is serving size. If the nutrition label on a carton of ice cream says 200 calories, you may think you’ve found a pretty good choice for dessert. However, if you usually eat three times the serving size for that product, then you need to consider that you’re actually consuming 600 calories, not 200. Pay attention to your portion sizes to get a more accurate measure of how many calories you’re consuming. Also, be wary of any misleading food labels.

However, dieters need to take into account more than just their calorie intake. A food may seem healthy if it has a lower calorie count, but if it contains high fat, cholesterol or sodium levels, it may not be a healthy choice. Look at the entire picture when purchasing foods based on calorie content; it’s important to take into account whether the food provides the nutrients, fiber or protein you need in addition to having a low to moderate calorie count.

While the concept of how calories are measured may be a little bit confusing, it’s important to remember one key concept: calories are energy, and if you’re consuming more than you need based on how much energy you use during the day, it will likely lead to weight gain. Watch your calorie intake and stay physically active to improve your overall health and maintain a healthy weight.


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