wikiHow to Calculate Basal Metabolic Rate
Three Methods:BMR CalculatorsCalculating BMR in MenCalculating BMR in WomenCommunity Q&A
If you're trying to lose, maintain, or gain weight, it's a good idea to start by calculating your Basal Metabolic Rate (BMR). Your basal metabolism is the amount of energy your body uses when it is completely at rest  it's simply the energy needed to operate your organs and keep you alive each day without taking any physical activity in to account. Your BMR is affected by a large number of variables  gender, age, height and weight are the most important, but your body fat percentage, diet, and exercise habits also play a role. Read on for an easy process that both men and women can use to calculate their BMRs.
Steps
1
Calculating BMR in Men

1Measure your height in centimeters. Generally, the bigger your frame is, the higher your BMR. All other things being equal, a tall man has more body tissue than a shorter man, which means he uses more energy each day simply by living. If you're not sure of your exact height, begin by getting an exact measurement of it. Use centimeters  BMR calculations are done in metric measurements.
 Stand with your back to a wall, with your heels touching the wall and your body straight. Have someone mark the height of the top of your head. Measure to straight up to that mark from the floor with a measuring tape to find your height.
 If you know your height in inches, you can multiply it by 2.54 to find your height in centimeters.

2Determine your weight in kilograms. If you haven't weighed yourself in a while, step on a scale. Generally, the heavier you are, the more energy your body uses every day. Weighing yourself is also a good idea if you're trying to gain or lose weight, as you'll need to be able to judge your progress an initial value.
 If you know your weight in pounds, you can multiply it by .454 to find your weight in kilograms.
 If you're trying to gain or lose weight, remember that your weight can fluctuate by 5 pounds or so throughout the day based on what you've eaten and drank, when you've used the bathroom, etc. If you're embarking on a journey to change your weight, weigh yourself about once a week at the same time of day while wearing similar clothing each time.

3Use the BMR equation for males. For men, the equation for calculating BMR is: BMR = 66 + (13.8 x weight in kg.) + (5 x height in cm)  (6.8 x age in years). This simple equation takes into account your height, weight, age, and sex. BMR increases with height and weight but decreases with age.
 The value for BMR in this equation is given in kilocalories per day. In everyday English, kilocalories are usually just called "calories"  you are probably familiar with calories from the Nutrition Facts section of food packaging.

4Know other factors that can affect your BMR. The BMR equation isn't perfect  it's just a convenient way of approximating your BMR. Your personal BMR will vary based on several other factors, including:
 Muscle mass. Leaner, more muscly bodies have higher BMRs than fatter bodies. A 200lb Olympic swimmer with a nearzero level of body fat will have a much higher BMR than a 200lb man with a moderate level of body fat.
 Bodily growth. People experiencing rapid growth (such as during puberty) will have higher BMRs, as will people growing new tissue after an injury.
 Body temperature. Elevated body temperature (as accompanies a fever) can increase BMR.
 Diet. Fasting or drastically dieting can reduce your BMR as the body compensates to run on less fuel.
 Heredity. Some people simply inherit their metabolism from their parents  if you've ever met someone who can eat endlessly without gaining weight, you've met someone who inherited a high BMR naturally.
2
Calculating BMR in Women

1Measure your height and weight. Just like in men, BMR varies greatly among women based on height and weight. For an accurate BMR measurement, get accurate values for your height and weight. Use metric values  centimeters for height and kilograms for weight  as the BMR equation assumes metric measurements.
 To convert your height in inches to centimeters, multiply it by 2.54. To convert your weight in pounds to kilograms, multiply it by .454 .
 If you're trying to lose or gain weight, remember to weigh yourself about once a week, at the same time of day each time. Your weight can fluctuate by 5 pounds or more each day simply from normal activity.

2Use the BMR equations for females. Because women often (but not always) have less lean body mass (found by subtracting the mass of fat tissue in the body from the total mass of the body) than men, they will generally have lower BMRs. The BMR equation for females takes this into account  it multiplies height and weight by smaller values. However, since women's metabolisms slow less drastically with age than men's, the value that age is multiplied by is also smaller. For women, the BMR equation is: BMR = 655 + (9.6 x weight in kg.) + (1.8 x height in cm)  (4.7 x age in years).
 As always, the value for BMR in this equation is given in "kcals (calories) per day."

3Know that pregnancy can affect BMR. Like men, diet, growth, body temperature, muscle mass, and heredity can influence a woman's BMR. However, women are unique in that pregnancy can also significantly impact BMR. Women who are pregnant (or breastfeeding) will have higher BMRs than women who are not. Nourishing an infant as it grows (and, later, producing breast milk) requires extra energy from the body  if you've ever noticed a woman's appetite increase when she becomes pregnant, you've seen this effect in action.
Community Q&A

If my BMR is 1290.2 then how many calories do I consume every day to lose weight?User ContributorJust decrease 200 calories per day. It is easier to just cut something than add everything up.

If my BMR is 1565.24, then how many calories do I consume every day to lose weight?User ContributorFor every 500 calories less than your BMR that you eat a day, you will lose around a pound a week (for you that would be 1065 calories a day). The other alternative is to eat your standard 1565 calories and burn the extra 500 per day by exercising.
Video
An educational video which which gives alternate formulas for calculating BMR. 
Tips
 Once you know your BMR, you can multiply it by an activity multiplier to calculate your Total Daily Energy Expenditure (TDEE), which estimates the total number of calories you expend in a day. The activity multiplier for sedentary people is 1.2, lightly active people (light exercise 1 to 3 times per week) is 1.375, moderately active people (moderate exercise 3 to 5 times per week) is 1.55, very active people (hard exercise 6 to 7 times per week) is 1.725, and extremely active people (hard daily exercise or training more than once in a day) is 1.9.
 If you have tested your body composition, you can use your lean body mass to calculate your BMR very accurately. Body composition is a measure of how much of your body weight is fat. All weight that is not fat is considered lean body mass. This equation does not change based on gender. BMR = 370 + (21.6 x lean body mass in kg)
Warnings
 The standard formula to calculate BMR is accurate for most people. However, it does not take into account the muscle to fat ratio. Therefore, it will underestimate the calories burned by a very muscular person and overestimate those burned by an obese person. If you are very lean or obese, you should use the formula that calculates BMR based on body composition.
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