The Bmr Calculator estimates your basal metabolic rate—the amount of energy expended while at rest in a neutrally temperate environment, and in a post-absorptive state (meaning that the digestive system is inactive, which requires about 12 hours of fasting). US Units.

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.
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.
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.
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.
BMR Calculator estimates the number of calories your body burns in a single day from its resting state based on your gender, age, height and weight. It utilizes the Mifflin-St Jeor equation to provide these calculations, as the American Council on Exercise (ACE) suggests it’s the most accurate method for estimating basal metabolic activity.