Calories and kilojoules are both units used to measure energy. Specifically, they measure the energy content in food. When looking at food labels, you’ll often see values listed for both calories and kilojoules.
But what is the actual relationship between calories and kilojoules? How can you convert between the two? Keep reading to find out.
The Relationship Between Calories and Kilojoules
First, it’s important to understand precisely what calories and kilojoules are measuring.
A calorie is a unit of energy. Specifically, 1 calorie is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius. Calorie counts on food labels actually refer to kilocalories. One food calorie (with a capital C) is equal to 1000 small calories (with a lower case c).
A kilojoule is another unit of energy. It is the SI unit for energy. One kilojoule is equal to the amount of energy required to generate one kilowatt of power for one second.
So how are calories and kilojoules related? Here is the conversion:
- 1 calorie = 4.184 joules
- 1 kilocalorie (food calorie) = 4184 joules
- 1 kilojoule = 0.239 food calories
As you can see, one kilojoule contains about 1/4 of a food calorie. Or in other words, it takes approximately 4.2 kilojoules to equal 1 food calorie.
Converting Between Calories and Kilojoules
Now that you understand the relationship between calories and kilojoules, let’s look at how to actually convert between them.
To convert calories to kilojoules:
- Multiply the number of calories by 4.184
For example:
100 calories x 4.184 = 418.4 kilojoules
To convert kilojoules to calories:
- Multiply the number of kilojoules by 0.239
For example:
418.4 kilojoules x 0.239 = 99.9 calories
So to summarize:
- Calories x 4.184 = kilojoules
- Kilojoules x 0.239 = calories
How Many Calories Are in 1000 Kilojoules?
Now we can easily calculate how many calories are in 1000 kilojoules:
1000 kilojoules x 0.239 calories/kilojoule = 239 calories
So in 1000 kilojoules, there are 239 calories. Or to put it another way:
- There are 239 calories in 1000 kilojoules
Calculating Kilojoules and Calories in Foods
When looking at food labels, you’ll usually see energy measured in both calories and kilojoules. You can use the conversions to calculate one if you only know the other.
For example, say a food item contains 300 calories. To determine how many kilojoules it has:
300 calories x 4.184 kilojoules/calorie = 1255.2 kilojoules
So that food item would contain 300 calories and 1255 kilojoules.
As another example, if a food item contains 836 kilojoules, to calculate the calories:
836 kilojoules x 0.239 calories/kilojoule = 200 calories
That food would contain 836 kilojoules and 200 calories.
Calorie and Kilojoule Counts of Common Foods
To give you an idea of typical calorie and kilojoule amounts in common foods, here is a table comparing the two:
| Food | Calories | Kilojoules |
|---|---|---|
| Apple, 1 medium | 95 | 396 |
| Banana, 1 medium | 105 | 439 |
| Orange, 1 medium | 62 | 259 |
| Carrot, 1 medium | 25 | 104 |
| Broccoli, 1 cup | 31 | 130 |
| Chicken breast, 3 ounces cooked | 140 | 588 |
| Salmon, 3 ounces cooked | 175 | 733 |
| Rice, brown, 1 cup cooked | 216 | 904 |
| Pasta, 1 cup cooked | 220 | 924 |
| Bread, whole wheat, 1 slice | 69 | 289 |
As you can see, most common foods provide calories in the range of 25 to 250 calories per average serving. Using the conversions above, you can calculate the number of kilojoules if you know the number of calories, or vice versa.
Calculating Your Daily Calorie and Kilojoule Needs
In addition to looking at the energy content of individual foods, you can also use calories and kilojoules to understand your total daily energy needs.
Here are some average daily calorie recommendations for different groups of people:
- Women: 1600-2400 calories per day
- Men: 2000-3000 calories per day
- Children: 1000-2000 calories per day
- Athletes or very active people: up to 4000 calories per day
To determine your personal daily calorie needs, you’ll need to consider your age, sex, height, weight, activity level, and health goals. There are various calculators online that can provide you with a good starting estimate.
Once you know your target calorie intake, you can use the conversions to determine the number of kilojoules. For example, if your target is 2000 calories per day, then:
2000 calories x 4.184 kilojoules/calorie = 8368 kilojoules
So a 2000 calorie diet would equal about 8400 kilojoules per day.
Sample Daily Calorie and Kilojoule Goals
Here are some sample calorie and kilojoule goals for different types of people:
| Person | Calorie Goal | Kilojoule Goal |
|---|---|---|
| 25 year old moderately active woman | 2200 | 9205 |
| 30 year old male office worker | 2400 | 10,042 |
| 40 year old lightly active woman | 1800 | 7531 |
| 18 year old high school athlete | 3000 | 12,552 |
| 55 year old sedentary man | 2000 | 8368 |
As you track your food intake, you can use this table to understand how your daily calorie and kilojoule totals compare to your estimated needs.
Should You Pay Attention to Calories or Kilojoules?
Now that you understand the relationship between calories and kilojoules, as well as how to convert between them, you may be wondering which one you should pay attention to when it comes to your diet.
The truth is, it doesn’t really matter which unit you focus on. The conversions between calories and kilojoules are fixed, so tracking either one will give you the same information.
In the United States, most food labels use calories. So for simplicity, it’s easiest to focus on calories if you live in the U.S. This will make it easier to interpret nutrition facts panels.
However, in most other countries, kilojoules are used instead of calories on food labels. So if you live outside the U.S., it likely makes more sense to track kilojoules.
No matter which unit you use, the principles of weight management remain the same. To lose weight, you need to create a calorie or kilojoule deficit by consuming fewer calories/kilojoules than you burn each day. To gain weight, you need a calorie/kilojoule surplus.
Benefits of Tracking Kilojoules Instead of Calories
While it doesn’t really matter which unit you use, some people find benefits to tracking kilojoules rather than calories:
- Kilojoules may be more intuitive to understand. A kilojoule represents energy generated per second, which is easy to grasp.
- Kilojoules allow for more precise measurements. One kilojoule is approximately 1/4 of a calorie.
- Kilojoules are the SI unit for energy and are used in most scientific contexts.
- Kilojoules may discourage obsessive calorie counting. The larger numbers don’t seem as emotionally charged.
Overall, it comes down to personal preference. Choose the unit that feels best for you, and don’t get too bogged down converting between calories and kilojoules. Focus instead on establishing healthy eating habits for long-term wellbeing.
The Bottom Line
Calories and kilojoules both measure the energy content in foods. They are related by the following conversions:
- 1 calorie = 4.184 kilojoules
- 1 kilojoule = 0.239 calories
So to be specific, there are 239 calories in 1000 kilojoules.
While kilojoules are the SI unit for energy, calories are still widely used for nutrition information in many countries including the United States. But regardless of which unit you choose to focus on, tracking your food intake and establishing healthy eating habits is what matters most for your health and wellbeing.
