Basal Metabolic Rate (BMR) Calculator
Disclaimer: The results given by this BMR calculation tool should be used only as a guide and should not replace medical advice. Please bear in mind that, when interpreting the results of this BMR calculator, other factors such as your lean body mass should be considered. You should always speak to a qualified Doctor or health professional for advice and guidance before making any dramatic changes to your lifestyle.
How to calculate your BMR
Your BMR is calculated by entering your height, weight and age figures into the BMR formula.
BMR formula
- For men: (4.536 × weight in pounds) + (15.88 × height in inches) - (5 × age) + 5
- For women: (4.536 × weight in pounds) + (15.88 × height in inches) - (5 × age) - 161
This calculation uses the Mifflin - St Jeor (1990) formula 1 and returns a figure known as your Basal Metabolic Rate (BMR). This figure represents the minimum number of calories your body requires to continue functioning. The body uses this energy to maintain basic functions such as breathing, cell production and temperature control.
It's worth noting that your BMR does not include energy expenditure for additional tasks, such as walking or eating. For this, you would turn to a Resting Metabolic Rate (RMR) calculation, which we will discuss later.
You'll notice that men and women have different formulae. This is due to the fact that men tend to have a higher percentage of lean body weight than women.
The above formula is the imperial version. If you prefer metric units, your formula looks like this:
- For men: (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
- For women: (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161
If you're in need of a quick conversion, you can use our trusty kilograms, stone and pounds converter. For height calculations, you can use the converter for cm to feet. We like to think we cater for all eventualities.
Example BMR calculation
Let's go through an example calculation. King Henry VIII's armour reveals that he had a 52 inch waist at the time of his death, aged 55. Standing around 6 foot 1 inches tall, we can estimate his weight at around 300lbs.
Henry's BMR calculation might look like this:
BMR = (4.536 × weight in pounds) + (15.88 × height in inches) - (5 × age) + 5
HENRY'S DETAILS ADDED
(4.536 x 300) + (15.88 x 73) - (5 x 55) + 5
MULTIPLICATIONS MADE
1360.8 + 1159.24 - 275 + 5
= 2250.04
So Henry's BMR would have been around 2250 at the time he died, which would have covered all his body's energy expending needs during a day of doing absolutely nothing whatsoever. Perhaps somebody could have mentioned this to the royal kitchen, who were providing at least 5000 calories a day for him to shovel down.
What is BMR?
BMR is short-hand for 'basal metabolism rate', but it could just as easily mean 'Breathing, Making cells, Resting' because that's what it really refers to. Your body requires a certain amount of energy from calories in your food in order to do all the clever body stuff it does behind the scenes, without you even needing to think about it. Everyone is different, and all bodies need a slightly different amount of calories to get them through the day, even if they are simply lying in bed and watching box-sets back-to-back. Your heart still needs to pump; your lungs still inflate and deflate; your hair grows and your wounds heal. This all requires energy.
BMR is one part of your total daily energy expenditure, which refers to all the calories burned in a typical day. Total daily energy expenditure (TDEE) includes BMR plus the number of calories that the body expends as a result of physical activity and digesting food.
An individual’s total daily energy expenditure (TDEE) is comprised of a number of different elements. The largest element is called Resting Energy Expenditure (REE), which refers to the basal metabolic rate (BMR) and accounts for between 65-75% of your daily energy expenditure.
The other element is known as Non-resting Energy Expenditure (NREE) and includes exercise activity thermogenesis (EAT), non-exercise activity thermogenesis (NEAT), and the thermic effect of food (TEF) 6
People will have a different BMR due to their genetics. Scientists also believe that other factors can influence BMR, such as body composition. However, metabolic processes are very complex and the scientific community is still learning what factors influence the differences we see between people. For example, recent evidence has suggested that people’s metabolic rate peaks during infancy and remains surprisingly stable between the ages of 20 to 60, where it starts to decline. 4
The best way to directly and accurately measure BMR involves using highly specialized lab equipment that measures heat changes from the body, which tells you how much energy it is using. However, these measures are very expensive and impractical for most people who want to know their BMR. Utilising a BMR formula is therefore a simple and more convenient way to estimate BMR without this equipment. Each algorithm has been tested against these direct BMR measures to check how accurate it is.
It is important to bear in mind that Basal Metabolic Rate calculations do not take into account for lean body mass, which will obviously have a factor of its own. Very muscular people, for example, will receive a figure that probably under-estimates their calorie needs and very overweight people will likely get a calculation that over-estimates their calorie requirements.
A study published in Nutrition Research in 2007 suggests that weight history and ethnicity may also affect the abiliy of the BMR formulae to estimate energy expenditure and predict dietary energy needs. 5
What is the difference between BMR and RMR?
Your BMR represents the energy requirements your body requires to perform basic functions such as pumping blood, breathing and temperature control. Your Resting Metabolic Rate (RMR) represents the number of calories your body burns while at rest and includes energy expenditure for essential, low-effort daily activities such as eating and walking to the bathroom.
You can get a rough calculation of your BMR by using a mathematical equation such as the Mifflin - St Jeor or Harris-Benedict formula. However, the most accurate way of obtaining a BMR measurement is to take a lab test. A BMR lab test is usually measured immediately after an overnight fast when you're completely rested. So, you would be careful to have no exercise in the previous 24 hours, no emotional stress, etc.
Although many people consider RMR to be a better indicator of daily energy requirements because it includes some activity that is arguably essential for living, BMR may be more accurate due to the additional restrictions in how it is measured. However, many people use BMR and RMR interchangeably as they are conceptually more or less the same.
BMR formulae
There are a number of different BMR equations in use today, from the more modern Mifflin - St Jeor formula, which was established in 1990, to the older Harris-Benedict formula from 1919 and the revised Harris-Benedict formula from 1984. You'll find different BMR calculators reference different formulae, so we've ensured you have access to all three in our calculator. Some evidence suggests that the Mifflin-St Jeor formula is more accurate than Harris-Benedict formula, which tends to overestimate the true metabolic rate bias and accuracy of resting metabolic rate equations in non-obese and obese adults. 3
The Harris-Benedict formula
The Harris-Benedict equation was the earliest BMR formula created and referenced, following its publication in 1919. As a reminder, the Harris-Benedict formula was revised in 1984, using new data in order to improve its accuracy. If you're wondering which one you want to use and reference in your calculations, it's worth reading our article about the BMR formulae here.
Calculating daily calorie requirement
Once you've worked out your BMR, you can calculate your daily calorie requirement by multiplying your BMR by one of the following activity level factors:
- If you are sedentary (little or no exercise)
Calories Per Day = BMR x 1.2 - If you are lightly active (light exercise or sports 1-3 days/week)
Calories Per Day = BMR x 1.375 - If you are moderately active (moderate exercise 3-5 days/week)
Calories Per Day = BMR x 1.55 - If you are very active (hard exercise 6-7 days/week)
Calories Per Day = BMR x 1.725 - If you are super active (very hard exercise and a physical job)
Calories Per Day = BMR x 1.9
Just having the knowledge of your BMR could give you a deeper insight into tailoring your diet for your own body's needs. Somebody with a clean bill of health could consume 90% of their BMR and already be on their way to weight loss, even before adding in extra exercise. Of course, as with anything that involves tinkering with your body, do seek medical guidance to ensure that the changes are safe and suitable for you.
Calculator created by Alastair Hazell and reviewed by Aaron Kandola, Ph.D.References
- Mifflin, MD; St Jeor, ST; Hill, LA; Scott, BJ; Daugherty, SA; Koh, YO (1990). "A new predictive equation for resting energy expenditure in healthy individuals". The American journal of clinical nutrition 51 (2): 241-7.
- The American Journal of Clinical Nutrition, Volume 40, Issue 1, July 1984, Pages 168–182. "The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass". https://doi.org/10.1093/ajcn/40.1.168
- Bias and accuracy of resting metabolic rate equations in non-obese and obese adults. Clinical Nutrition, Volume 32, Issue 6, 2013, Pages 976-982, ISSN 0261-5614
- Daily energy expenditure through the human life course. https://www.science.org/doi/10.1126/science.abe5017
- Ability of the Harris-Benedict formula to predict energy requirements differs with weight history and ethnicity. Nutrition Research, Volume 27, Issue 4, 2007, Pages 194-199, ISSN 0271-5317,
- Trexler, Eric & Smith-Ryan, Abbie & Norton, Layne. (2014). Metabolic adaptation to weight loss. Journal of the International Society of Sports Nutrition. 11. 7. 10.1186/1550-2783-11-7.
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