Understanding calories

Calories are a measure of the amount of energy in food. Knowing how many calories are in our food can help us to balance the energy we put into our bodies with the energy we use. That’s the key to a healthy weight.

An average man needs around 2,500kcal (10,500kJ) a day. For an average woman, that figure is around 2,000kcal (8,400kJ) a day. These values can vary depending on age and levels of physical activity, among other factors

We measure the amount of energy contained in an item of food in calories, just as we measure the weight of that item of food in kilograms.

If you’re trying to lose weight, it’s a good idea to eat less and be more active. Eating less is important when you're trying to lose weight, even if you already have a balanced diet.

You can check whether you’re a healthy weight by using our BMI healthy weight calculator.

Calories and energy balance

When we eat and drink, we’re putting energy (calories) into our bodies. Our bodies then use up that energy, and the more physical activity we do, the more energy (calories) we use.

To maintain a stable weight, the energy we put into our bodies must be the same as the energy we use by normal bodily functions and physical activity. If there are some days where we put in more energy than we use, then there should also be days where the opposite is true, so that overall the energy in and energy used remain balanced.

Weight gain occurs when we regularly put more energy into our bodies than we use. Over time, that excess energy is stored by the body as fat. Research shows that most adults eat and drink more than they need, and think that they are more physically active than they are.

Checking calories in food

Knowing the calorie content of foods can be a useful tool when it comes to achieving or maintaining a healthy weight. It can help us to keep track of the amount of energy we are eating and drinking, and ensure we're not consuming too much.

The calorie content of many foods is stated on the packaging in the nutrition label, which you will often find on the back or side of the packaging. This information will appear under the "Energy" heading. The calorie content is often given in kcals, which is short for "kilocalories", and also in kJ, which is short for "kilojoules".

A "kilocalorie" is another word for what is commonly called a "calorie", so 1,000 calories will be written as 1,000kcals.

Kilojoules are the metric measurement of calories. To find the energy content in kilojoules, multiply the calorie figure by 4.2.

The label will usually tell you how many calories are contained in 100 grams or 100 millilitres of the food or drink, so you can compare the calorie content of different products. Many labels will also state the number of calories in "one portion" of the food. But remember that the manufacturer’s idea of "one portion" may not be the same as yours, so there could be more calories in the portion you serve yourself.

You can use the calorie information to assess how a particular food fits into your daily calorie intake. As a guide, the average mans needs 2,500kcal (10,500kJ) to maintain his weight, and the average woman needs 2,000kcal (8,400kJ).


Calorie counters

There is a wide range of online calorie counters. We can't verify their data but they can help you track your calories. Examples include:


Some restuarants put calorie information on their menus, so you can also check the calorie content of foods when eating out. Calories should be given per portion or per meal.

You can learn more on our page on food labels.

Burning calories

The amount of calories people use by doing a certain physical activity varies, depending on a range of factors, including size and age.

The more vigorously you do an activity, the more calories you will use. For example, fast walking will use more calories than walking at a moderate pace.

If you’re gaining weight, it usually means you’ve been regularly eating and drinking more calories than you've been using through normal bodily functions and physical activity.

To lose weight, you have to tip that balance in the other direction. You must start to use more energy than you consume, and do this over a sustained period of time.

You can do this by making healthy changes to your diet so that you eat and drink fewer calories. Learn more on our pages on food and diet.

The best approach is to combine these changes with increased physical activity. Find out if your physical activity levels need a boost with our fitness tool.

You can learn more about making healthy changes to your diet in our lose weight section.

You can also talk to your GP or practice nurse to get more advice on achieving the right energy balance and losing weight.

Page last reviewed: 25/08/2014

Next review due: 25/08/2016


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The 14 comments posted are personal views. Any information they give has not been checked and may not be accurate.

Lancaster64 said on 24 May 2015

This is wholly misleading/incorrect. A calorie is a unit of heat and heat is generated in the mitochondria.

If a mars bar is placed in a freezer it will contain less heat.

It is the accessibility of the energy that is the issue.

This is oversimplified and incorrect.

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leica said on 11 October 2014

It would be really useful for the calorie checker and the PDF guide to be incorporated into a IOS / Android app - I'd trust something produced by the NHS not to have any commercial agenda.

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LiveHealthyChick said on 29 January 2014

Doikosp I totally agree with you. Portion control is key! If you absolutely feel compelled to count calories doing so in the beginning of your healthy journey will work but soon after you will get a feel for the food items that are healthier for you. Here is a great article that tells you the history of the Calorie and explains what empty calories are http://www.simplelivehealthy.com/2014/01/22/living-healthy-for-beginners-what-are-calories/

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SteveWright said on 26 January 2013

The problem with most calorie counting websites, and even with the information that is displayed on the labels of food packaging, is that it is not entirely clear. Many people do not know how to interpret the information that is in front of them because it has not been simplified. This is why I created my own website that tells people the calories found in all of the generic foods that we eat, and beverages that we drink. It does not include tables, graphs, labels and all of the information that can confuse somebody looking for basic calorific values.
I agree that obsessively counting calories is not the way forward, but having an understanding as to roughly how many you are consuming throughout a day in comparison to the total you need in order to lose, maintain or gain weight is critical. At least then people can actually make informed dietary decisions instead of either under, or over eating and having some sort of weight problem, and wondering why this is.
For those that don't want to read every label, perhaps you will find this useful.


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Doikosp said on 19 January 2013

By the way, iIf you're looking for the calories of a specific food you can quite often just put the query into a search engine and find it online. E.g. "Cod calories",

Most fruit are pretty low, e.g. oranges are about 62 kcal per 100g. (though Satsumas are only about 26 kcal per 100g.

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Doikosp said on 19 January 2013

REALISTICALLY, obsessive counting of calories isn't needed, or helpful, for losing weight. Having a pretty good sense of the calorie count of what you're eating is both necessary had very helpful.

And 'portion control' is also important.

But most people on a diet know if they've overdone it one day, because the scales tell them the next!

And as you get used to checking labels, and reading recipes on line, etc., you build up a rough idea about the things that you personally eat.

My tack is to weigh myself each morning before eating or exercise, after my first wee! If it's less than yesterday - great! If it's the same, or even up a bit - ho hum. The more important thing is to consider it over the week. If this weekend I'm lighter than last weekend, then I'm still going in the right direction. If not, then I have to re-work something.

Dieting also takes a bit of getting used to - I'm losing it a bit too quickly right now, but as I get better at it all, I can adjust that more knowingly and sensibly.

And you learn day by day. I usually have a scone for elevenses at work and I've just realised that it's probably a lot more calories than I thought (about 350 - 400). So, I may just replace that with something like fruit, or rice cakes, or something.

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seafreak said on 05 September 2012

I agree with most of the above comments. All the so-called free calorie counter websites I have tried want you to sign up for something, whereas all I want is a good chart of the most popular fresh and processed foods, with their calorie rating. I know everyone is different, which is why I want to find a way of losing weight that will suit me and not make my life miserable. It would be very helpful if the NHS could comment on the recent BBC programme about the "5 days off, 2 days on" diet. A list of typical meals of 600 calories or under would be just the thing. And we need something more encouraging about exercise. Those of us who don't care for sports and find running deeply boring are being made to feel guilty, as if sport is in itself virtuous. It isn't, and a lot of the time it just causes discord and bitterness. I do regular water aerobics, which I would reccommend to anybody because you don't feel nastier at the end of it than you did at the beginning. Many people lead sedentary lives because that is their job and, which is more to the point, that is where their interests and their talents lie. I want to be fit- i.e. I want to have the strength and capacity that fits the life I lead. Please, you NHS advisers, don't keep assuming it's all about fashionable clothes or marathons. As far as I'm concerned it's a question of not having to keep bothering about my body all the time when I've got other and more interesting things to think about.

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Dasuto said on 08 August 2012

I am surprised and disappointed that this NHS site does not include a free calorie counter. On other sites you appear always to need to sign up to some commercial selling site to get access to a calorie counter. Dasuto.

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kathleenhelen said on 11 May 2012

I agree with Grumpya and Joanann- this website is totally ineffective in providing the necessary information we are looking for: my husband wants to lose 2 stone and asked me how many calories are there in an orange? I don't know!Yes, we can all read the packets to find out how many calories there are in a preprepared meal- we've been doing that for years! But what about a free booklet that gives us the calories in real foods? Another page showing average calorie 'burn' in common activities, like vaccuuming the carpet/ mowing the lawn/ painting the guest room etc?Without signing up to a commercial weight
loss programme? Isn't that what this website should be doing? And is anyone at the NHS actually reading these comments, or are they simply there for people to 'let off steam'?

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tom91 said on 19 April 2012

This whole interest in eating less calories and burning more erks me

1. They say that Carbs and protein have 4kcal per gram and fat has 9kcal per gram. They are just averages. If you burn one fatty acid and compare it to another you will get potentially very different results.

2. There is a metabolic cost to metabolising and digesting food. Lower quality food will require more energy to process and metabolise it.

3. There is an endocrinological response to eating food. The hormones released will differ based on the type, quality and quantity of the food you eat. This hormonal response will govern whether you store the food short term or long term, how fast the food is absorbed etc.

4. If someone is metabolically deranged then they can't eat less and exercise more because thier biochemistry is telling them not to. If a person is leptin resistant (from eating too much sugar / every overweight person) then their brain will think they are starving. So their body will expend less calories and try and consume more.

5. Reducing caloric intake chornically will be interpreted by your body as starvation and this will a stress response. Cortisol will be released and you will hold onto fat and lose muscle mass.

So to summarize

- Food quality > food quality

- A calorie is not a calorie

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Crose1xbose said on 14 April 2012

None of the information on this page is of any relevance to anyone trying to lose weight safely for a long time period, I used to be very overweight (19 stone, now 12 stone) and have had to use unreliable organisations advice (often far from accurate and often mixed) to get any results, I feel let down by the NHS on the account that the information here is very basic, what about those who work in a active job, those who are disabled and methods of slowly building up fitness? also does not mention the fact that fat has around 7 calories per gram whilst carbohydrates and protein have only 4 calories per gram hence the benefit of a low-fat diet, also metabolic rate and ways of safely increasing it, for instance the more muscle mass you have the more calories you burn, how much protein should be increased (whist underttaking a exercise program) to prevent loss of muscle tissue thereby peventing the slowing of metabolism and increasing weight loss, seems like I know more about this than you do NHS.

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grumpya said on 24 March 2012

Having trawled through 3 pages of Bing looking for an nhs or gov advice page on counting calories I found this very disapointing. I have 11 stone to lose & have tried all the money making clubs which don't work for me I want to count calories. All morning on the news they have been talking about how the gov have been negotiating with food companies to reduce the calories in foods, & about losing weight by reducing calories. I would have liked links to a page of calorie values & some advice on how many calories I should be consuming to lose weight. I know that very overweight people start off on more calories than girls who want to lose 7lbs but don't know how many I should have especially as I will have to stick to it for a year or 2 to get to target

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FAO said on 24 June 2011

I agree completely with Joanna, it is very disappointing that there is no calorie information on the website especially when the NHS is campaigning healthy eating. I cook almost 99% of my food and I would like to know the constituents of the food. The United states has got USDA national nutrients Database and I expect that we would also have something similar in the UK.

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Joanann said on 10 October 2010

I was disappointed in the website as I did not find what I was looking for. I had hoped to find a list of calorie values of common foods. I currently eat a healthy diet and on the whole avoid ready meals which often have too much salt in them. The only suggestion made for finding out calorie values was to look at the values given on packaging. Many foods such as meat and fish bought from a butcher or fishmonger do not come in packaging. Nor do these items have calorie values on them from supermarket fish or meat counters.

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