What does ‘calories-in vs calories-out’ actually mean?

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If you have been researching into ‘how to lose weight’ or ‘how many calories do I need to eat’, surely you’d have come across the saying ‘calories-in vs calories-out’. But what does it actually mean?

What are calories?

Calories are normally referred to as calories (cal) to make it simple for people to understand but in reality, calories are actually kilocalories (kcal). Calories are a unit of energy, 1 calorie is the amount of energy it would take to heat up the temperature of 1kg of water by 1 degree Celsius (Scott, 2019). Whereas, a kilocalorie refers to the amount of heat required to increase the temperature of 1kg of water by 1 degree celsius. 1 kilocalorie is equivalent to 1000 calories (Scott, 2019). In other words, 1 calorie = 1000 kilocalories.

It is kilocalories that you actually see on food labels.

When you hear someone mention calories, they are referring to a unit of measurement. For example, similarly to how your weight is measured with Kg.

Let’s dive into a little more detail.

As we mentioned earlier, a calorie is a unit of measurement for energy. Foods can be categorised into three macronutrients:

  • Carbohydrates – 4 calories per 1 gram
  • Protein – 4 calories per 1 gram
  • Fat – 9 calories per 1 gram

The units above show you how many calories each macronutrient provides. In other words, the values above show you the amount of energy each macronutrient provides.

What are calories-in

Calories-in refer to the amount of calories you will consume per day. You’d need to know what your maintenance calories are in order to eat less than that to lose weight or eat just that to maintain your weight. This is also known as a caloric-deficit.

What are calories-out

How many calories you burn per day. You’d need to know what your maintenance calories are in order to burn a specific amount of calories if you are looking to lose weight. This is also known as a caloric surplus.

What are your maintenance calories?

Maintenance calories are the amount of calories your body requires to maintain your current weight. You’d need to calculate your maintenance calories in order to figure out how many calories-in you require to lose or gain weight.

How to calculate your maintenance calories?

You will firstly need to calculate your BMR (Norton and Baker, 2019):

MEN – (88.362 + (13.397 x body weight in KG) +4.799 x Height in CM) – (5.677 x age) = BMR

WOMEN – 447.593 + (9.247 x body weight in KG) + (3.098 x Height in CM) – (4.330 x age) = BMR

For example, the equation for a 24-year-old woman who weighs 52kg and is 152cm in height is as follows:

447.593 + (9.247 x 52) + (3.098 x 152) – (4.330 x 24)

447.593 + 480.844 + 470.896 -103.92 = 1295.413 (BMR)

Then, you take the BMR values and multiply them by your activity factor (Norton and Baker, 2019):

  • Sedentary – 1.2 (work at an office and do not exercise)
  • Light Activity – 1.375 (Either you work in an active occupation eg. Waitressing or you work in an office job but sometimes exercise)
  • Moderate Activity – 1.55 (You may work in a sedentary job but exercise very regularly or you may simply be working at a physically demanding job eg: Labourer
  • Very active – 1.725 (You may exercise most days of the week and you may work in an active occupation)
  • Extra active – 1.9 (You exercise every day and you work in a physically demanding job)

Taking it back to our example, let’s say our hypothetical woman whose BMR was 1295.413 (you can also round this figure up), is moderately active. So we will now multiply 1295.413 (BMR) by 1.55 (value for moderate activity) to generate maintenance calories.

1295.413 x 1.55 = 2007 maintenance calories (rounded up)

How many calories are in 1lbs of body fat?

In order to gain or lose 1lbs of body fat, you need to understand how many calories 1lbs of fat contains. 1lbs of fat contains 3500 calories.

So what does ‘calories-in vs calories-out’ actually mean?

Calories-in refer to the amount of calories you consume per day. Every time you eat, check the label on the food packaging to see how many calories that food contains. If you are looking to lose weight, calculate your maintenance calories, like we did above, and reduce those calories by 500 and consume those reduced calories to lose 1lbs of fat per 1 week. Also called caloric deficit.  The reason behind this is, like we mentioned earlier, 1lbs of fat is 3500 calories. So, if you reduce your maintenance calories per day, over 1 week, you’d have lost 3500 calories. And TAH DAH! 1lbs of fat lost.

It is not recommended losing any more than 1lbs of fat per week as it will not be sustainable.

What if I want to gain weight?

Gaining weight works similarly to losing weight. If you want to gain 1lbs of weight, you’d need to increase your daily calories by 500. By exercising regularly, more of the weight you gain will be muscle mass but it is impossible to gain muscle mass only. If you’d like to minimise the amount of fat you gain during your bulking time, you should maybe gradually increase your daily calories. Instead of 500, maybe start at 200 calories, and work your way up.

What about calories-out?

Calories-out refer to the amount of calories you burn per day. This part can be a little complicated. It is not just the amount of calories you burn during exercise but it also refers to the amount of energy your body can burn on its own without exercise. Also known as metabolism. Metabolism is the amount of calories your body can use for energy during a resting day. For example, when you sleep you will burn an amount of calories thanks to your metabolism. Some people may burn more calories than others but this also depends on how good their metabolism is.

If one day, you over consume you calories, not all is lost! So do not enter the ‘cheat day it is’ mode! If this does happen, go to the gym or do some sort of exercise to burn the calories you have over consumed. As long as you burn those calories within 3 hours of consuming that meal, you will still be on track to your goal!

How to calculate calories in food?

Normally, any food you purchase will have a label on the packaging. Usually, these labels will show you calories per 100g of that product. In order to calculate the calories in  food you ate, you can do the following:

  • Read the label and if you are planning on eating that whole food then calculate the calories found in 100g by the amount of grams that product contains. For example, a chocolate bar label is showing that per 100g of the chocolate bar you will eat 300 calories but the chocolate bar is 230g. Therefore, I will take 300 (calories per 100g) and multiply by 2.3 (grams in the whole product) – 300 x 2.3 = 690 calories.
  • Alternatively, what you can do is take the calories per 100g divide it by 100 to get how many calories is in 1 gram of the product. Then multiply it by the amount of grams you consumed. For example, you ate a packet of crisps that was 23g but the packaging shows you calories per 100g (95 cals). You would take 95 (calories per 100g) and divide by 100 to get 1 calorie per 1 gram (95 / 100 =0.95). Then, take your answer (0.95) and multiply it by the amount of grams you ate – 0.95 x 23 (grams per packet you ate) = 22 calories (rounded up).
  • If you wish to meal plan, you will need to get a wee kitchen scale to calculate how many grams you are putting on your plate or into a container. There is no other way around it.


Calories-in is the amount of calories you consume per day and calories-out are the amount of calories you burn per day. In order to know how many calories you need to consume per day to lose or gain weight, you’d need to calculate your maintenance calories first.

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Norton, L. and Baker, P. (2019). Fat loss forever. 1st ed

Scott, J. (2019). Calorie Definition and Why We Count Them. [online] Verywell Fit. Available at: https://www.verywellfit.com/what-is-a-calorie-and-why-should-i-care-3496238 [Accessed 1 Nov. 2019].

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