BMR Calculator is a simple tool that helps you calculate how many calories your body would need if you were only to rest for the whole day. Based on your age, height, weight, and gender, the Basal Metabolic Rate Calculator returns your BMR score. Keep reading to find out what is BMR, how to calculate BMR, learn more about Mifflin St Jeor equation and other BMR formulas. We will also show you the differences between calculating BMR for a man and estimating BMR for a woman.

For more inquisitive readers we have prepared a theoretical background on how to distinguish Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR). We also have written what factors affect our BMR. Do we have an influence on our BMR? Keep reading to find an answer!

What is BMR? – BMR definition

Basal Metabolic Rate is the amount of energy a human body uses in an entirely resting state. It's the amount of energy, your body needs, to support its vital functions. Those include breathing, blood circulation, controlling body temperature, brain and nerve functions among others. Organs using the most of energy in such condition are the central nervous system and the liver. What's interesting, more energy is consumed by processes regulating the fluid volumes and ion levels than an actual mechanical work of contracting muscles (e.g., breathing). Our body needs to correct concentrations and amounts of different substances in various areas of our organism to preserve homeostasis (a state of the steady internal conditions). Sometimes it requires transporting substances through barriers (e.g., cell membranes) and against a concentration (or molarity) gradient. It means that particles are transported from space, with their low concentration, to space with their higher concentration. On a scale of our entire body, it takes a lot of energy. It also explains why our central nervous system consumes so much energy in terms of Basal Metabolic Rate. When a neural impulse is conducted, a lot of different ions change their location. Afterward, they need to be transported back to their original place.

On a regular basis, people use more energy than their Basal Metabolic Rate. It is because they also perform their normal daily activities. Walking, running, working, talking, and even digesting are actions that require some extra energy not included in the Basal Metabolic Rate. To achieve such low expenditure of energy, you have to be physically and psychologically inactive. In other words, you cannot use any muscles nor think intensively. You need to be as much relaxed as it is possible. Other necessary criteria include staying in an environment with thermal comfort and not eating for a certain period. The latter condition assures that you will not be digesting. In a scientific setting, BMR is often measured after a period of sleep.

Your BMR accounts for about 60% to 75% of your Total Energy Expenditure (TTE), depending on your lifestyle and activity level. The Total Energy Expenditure is the total number of calories you burn every day. The rest of your TTE comes from the physical activities (walking, talking, eating, etc.) and food digestion. Physical activities account for about 20% of Total Energy Expenditure but can vary a little bit depending on the number and intensity of exercises you perform regularly. The food digestions, or as some say postprandial (after-meal) thermogenesis, uses around 10% of TTE. BMR tends to get lower with aging and decrease in lean body mass. On the other hand, increasing your muscle mass will most likely also increase your BMR. We write more about different things having an influence on the Basal Metabolic Rate in the factors affecting BMR paragraph.

Basal Metabolic Rate Calculator

BMR Calculator stands for the Basal Metabolic Rate Calculator. Basal metabolism is a set of chemical reactions, happening in everyone's body, required to maintain its living state. We have covered this topic thoroughly in the previous paragraph (What is BMR? – BMR definition). Knowing what your Basal Metabolic Rate is, can help you estimate the minimal intake of calories you require for the living, and thus evaluate the total number of calories you should provide to your body daily. Remember, you need to add, to the number of calories calculated with our BMR calculator, your energy expenditure (in calories) on other activities like walking, talking, etc. If you account something more for digestion (about 10%), you will get your daily Total Energy Expenditure. These informations may become a basis for your weight loss plan.

But how to use the Basal Metabolic Rate calculator?

  1. Firstly, measure your weight and type it in the Weight field of our calculator.
  2. Secondly, check your height and input it into the Height field.
  3. Now, input your age into the Age field. Please note, that the age value has to be in years.
  4. The last thing to do is to select your gender. You can choose between male and female. In the next paragraph, you will see that it slightly changes the formula for Basal Metabolic Rate.
  5. Well done! You have followed correctly through all the steps, and now our Basal Metabolic Rate calculator will show your minimal caloric intake for you!

If you are wondering what your ideal weight should be, visit our ideal weight and body mass index calculators. Would you like to change your present weight? Our macro and protein calculators will tell you what to eat and in what quantity. Finally, our calories burned calculator will keep you motivated during heavy training sessions.

How to calculate BMR - the BMR formula

There are multiple formulas used to calculate BMR. Nowadays, the Mifflin-St Jeor equation is believed to give the most accurate result and it's what we use in this calculator. This BMR formula is as follows:

BMR (kcal / day) = 10 * weight (kg) + 6.25 * height (cm) – 5 * age (y) + s (kcal / day),

where s is +5 for males and -161 for females.

We also have calculators that determine your Basal Metabolic Rate based on other formulas. For a long time, the most common way to calculate your Basal Metabolic Rate was Harris-Benedict equation. It was initially published back in 1919, and for over 70 years it was considered to be the best Basal Metabolic Rate formula available. Later on, it was replaced with another Basal Metabolic Rate formula that turned out to be even more accurate – Mifflin St Jeor Equation. Nevertheless, you can find the Harris-Benedict Equation used in many BMR Calculators until the present day. It is being slowly but consistently replaced with the new formula, though.

The third known equation is Katch-McArdle formula, used to tell the Resting Daily Energy Expenditure (RDEE).

In our Basal Metabolic Rate Calculator, we used the most commonly used Mifflin St Jeor Equation to give you the most accurate BMR score.

BMR for man calculation – an example

In this paragraph, we will deal together with an example of BMR calculation for a man. We will have to use this BMR for man formula (Miffin and St Jeor BMR equation for the man):

BMR (kcal / day) = 10 * weight (kg) + 6.25 * height (cm) – 5 * age (y) + 5 (kcal / day)

Let's suppose that you want to calculate BMR for a 60 years old man, who has 5 feet and 4 inches of height, and weighs 150 pounds.

  1. In the beginning, we have to change the values from the imperial to the metric system. We have to do that because the BMR formula has been designed to be used with the metric system only. Five feet and four inches of height equal to around 162.56 centimeters of height, while 150 pounds weigh the same as 68.04 kilograms. Luckily, we measure the age the same way in both systems. Notice that you can type into our calculator value of a certain unit (e.g., feet), and then change the unit (e.g., into meters). Our calculator will perform the transformation for you. This option works in the majority of our calculators, and sometimes it may come very handy.

  2. Now, we can input all the data into the BMR for man equation:

    10 * 68.04 + 6.25 * 162.56 – 5 * 60 + 5

  3. The last thing to do is to solve the equation:

    10 * 68.04 + 6.25 * 162.56 – 5 * 60 + 5 = 680.4 + 1016 – 300 + 5 = 1401.4 (kcal / day)

  4. And it's done! It wasn't so bad. You now know how to calculate BMR by hand, but it is still probably much easier to just input the data into our BMR calculator.

BMR for woman calculation – an example

This time we will try to calculate BMR for woman. We are going to use a slightly different formula - Miffin and St Jeor BMR equation for woman.

BMR (kcal / day)= 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161 (kcal / day)

As you may have already noticed, the only difference between these two formulas is their last part. We add 5 kcal per day for every man and subtract 161 kcal per day for every woman.

Now, let's focus on an exemplary woman that is 25 years old and measures 5 feet and 8 inches of height. Her weight is 132 pounds. We can proceed to the calculations.

  1. Firstly, we need to transform the values from the imperial system to the metric system. You can use the same method we have mentioned in the last paragraph. Five feet and eight inches equal to 172.72 centimeters. We transform 132 pounds of weight into 59.87 kilograms. Age, again, stays the same.

  2. Secondly, we can now input acquired values into the BMR for woman equation:

    10 * 59.87 + 6.25 * 172.72 – 5 * 25 - 161

  3. At last, we can solve the equation itself:

    10 * 59.87 + 6.25 * 172.72 – 5 * 25 - 161 = 598.7 + 1079.5 – 125 – 161 = 1392.2 (kcal / day)

  4. As always, we encourage you to check the result with our BMR calculator. As we have made a few approximations to make the calculations by hand easier, there may be a small difference between the results. But don't worry! It is so small that it will not affect any diet plan.

BMR vs. RMR

When making your research on Basal Metabolic Rate, you may also encounter a term RMR. It stands for the Resting Metabolic Rate. As these terms sound very similar and have a close meaning, it is very easy to get confused. But no worries, we will explain it to you shortly. Resting Metabolic Rate, much like BMR, is also a measure of a human body energy expenditure without performing any additional activities (so basically at rest). However, there is a slight difference. Resting Metabolic Rate also includes the energy used for digestion of food.

Our organism has to use some energy to transform the food it is receiving into substances that can be used for its purposes. As we have already mentioned in the what is BMR? – BMR definition paragraph, food digestions uses around 10% percent of Total Energy Expenditure. Because of that, RMR has a higher value than BMR. We use the modified Harris-Benedict formula, instead of Mifflin St Jeor equation, to calculate Resting Metabolic Rate. For more information on this topic, and an automatic estimation of your RMR visit our Resting Metabolic Rate calculator.

Factors affecting BMR

Each cell, tissue, and organ of your body requires a constant supply of energy to survive. It is then logical that the more your body weighs, the more tissues it has, and the more kilocalories it needs. With increasing weight, your Basal Metabolic Rate will rise as well. However, BMR doesn't depend solely on weight. In many different studies, researchers found other factors affecting our Basal Metabolic Rate value. Here, we mention some of them:

  1. FFM – standing for fat-free mass. It is the weight of your body without the mass of fat tissue. If you think about it, it will start to sound reasonable. Your muscles, even at rest, use up a lot more of energy than the fat tissue. In fact, the main function of fat tissue is to preserve energy in the form of fatty acids. A big ratio of fat-free mass to fat-mass increases BMR. Two men may weigh 220 pounds. However, the weight of one of them may be thanks to big muscles developed during workouts, while the weight of the other one may come from the fat tissue in his belly. Without a doubt, the first gentleman will have a significantly higher Basal Metabolic Rate.
  2. FM – shortcut for fat-mass. As the name suggests, it is the weight of all the fat in our body. Although much lower, fat-mass also has an influence on our Basal Metabolic Rate.
  3. Age – during childhood, your Basal Metabolic Rate increases with each year as you grow up and your weight rises. In contrary, BMR of adults tends to decrease as they get older. Researchers attribute this mainly to the change of human body compositions as it ages. The fat-free mass drops down, and thus, the Basal Metabolic Rate becomes lower.
  4. Gender – men have statistically higher BMR than women. The reason is that their fat-free mass is on average also higher. This is why the creators of equation estimating BMR added special adjustments to the equation for each sex (plus 5 kcal/day for man, and minus 161 kcal/day for woman).
  5. Genetics – every person is slightly different regarding their BMR. Some of these differences can be explained by the rate of your metabolism encrypted into your DNA code.
  6. Exercises – especially body-building exercises (e.g., bench press). When you develop your muscles, you increase the weight of your fat free mass. As we have already mentioned, fat free mass is responsible for the majority of your BMR (see the first point of this list). Remember not to overextend when exercising. Our max heart rate calculator may be useful here since it shows you your maximal healthy heart rate.
  7. Body temperature – your BMR increases as the temperature of your body rises. In a higher temperature (e.g. during a fewer) various chemical processes in your organism happen faster. Because of that, there is a higher demand for energy, and thus your BMR increases.
  8. Temperature of environment – in colder temperatures your body needs to create more heat to preserve its proper temperature. This leads to an increase of BMR.
  9. Hormones – hormones are substances produced by many glands of your body. Their main task is to regulate functioning of other organs and tissues. The most interesting gland in terms of BMR modification is, without a doubt, thyroid gland. Hormones excreted by this gland are responsible for regulating the rate of your metabolism. When they are in high concentration in blood, your BMR increases and vice versa.
  10. Pregnancy – when a woman is pregnant, there is another organism developing inside her body. Naturally, we are talking about the fetus (the baby). It has its own metabolism and BMR. Because it receives all the nutrition from its mother, we need to add its BMR to BMR of its mother when calculating the basic required calorie supply. If you are pregnant, visit our due date calculator and find out when to expect the childbirth.
Mateusz Mucha and Kacper Pawlik.

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