# BMR Calculator

This BMR calculator estimates the Basal Metabolic Rate (BMR) of a person based on age, sex, body weight, and body height. This calculator is intended for adults between the ages of 18 and 80 years old. To use the calculator, please provide your age, weight, height, activity level, and click the "Calculate" button.

## What is BMR?

Even while at rest, your body still expends energy to perform functions such as breathing, circulating blood, processing nutrients, producing cells, and more. Your basal metabolic rate (BMR) is the amount of energy that your body requires in order to perform these base functions. This is also a good estimate of your resting energy expenditure (REE), which is the amount of energy you burn over time while at rest. BMR and REE are often used interchangeably, because while their definitions differ, they can be used to estimate each other.

Because BMR requires strict conditions to properly measure, such as being awake but completely at rest, it is usually estimated instead. A significant amount of research has been done surrounding estimating BMR, and a number of different equations have been developed for this purpose, such as the Mifflin St Jeor Equation, the Harris-Benedict Equation, and the Katch-McArdle formula. The equation used by this calculator to estimate BMR is the Mifflin St Jeor Equation (discussed below).

BMR is commonly used as a way to measure the number of calories you need to consume per day in order to lose weight, gain weight, or maintain your weight. For the average person,

- to lose weight, consume fewer calories than your BMR.
- to gain weight, consume more calories than your BMR.
- to maintain weight, consume the same number of calories as your BMR.

Everyone's circumstances are different however, and while the above works in theory, it may not work for everyone.

## How is BMR estimated?

BMR is estimated using several different equations. The calculator on this page uses the Mifflin St Jeor equation. For those who have an accurate estimate of their body fat percentage, the Katch-McArdle formula may provide a more accurate estimate of BMR. The Mifflin St Jeor equation uses the height (H in centimeters), weight (W in kilograms), and age (A in years) of a person to estimate BMR, and slightly differs for men and women.

For women:

BMR = 10W + 6.25H - 5A - 161

For men:

BMR = 10W + 6.25H - 5A + 5

For example, a 33-year-old woman who weighs 55 kg and is 160 cm tall has an estimated BMR of:

BMR = 10×55 + 6.25×160 - 5×33 - 161 = 1224

This means that while completely at rest, this woman would burn 1224 calories worth of energy. Realistically, we are not usually completely at rest, so the number of calories we actually burn throughout the course of a day is most likely higher than this number.

## Daily calorie needs

The number of calories a person needs in a day varies widely depending on a number of factors such as age, weight, height, sex, physical activity level, general health, and more. The U.S. department of Health estimates that adult males require approximately 2000-3000 calories per day to maintain weight, while adult females require approximately 1600-2400. The amount that a person needs in a day is also dependent on the amount of activity they get on a given day, so it varies day by day, and is difficult to measure. One way in which it is estimated is using BMR and typical activity level.

The number of calories we need in a day, referred to as the total daily energy expenditure (TDEE) can be estimated using the following formula:

TDEE = BMR × activity factor

The activity factor is a constant based on the amount of exercise you normally get in a week (activity level), as shown in the table below:

Activity level | Activity factor |
---|---|

Sedentary (no exercise) | 1.2 |

Light (exercise 1-2 days/week) | 1.375 |

Moderate (exercise 3-5 days/week) | 1.465 |

Active (exercise 6-7 days/week) | 1.55 |

Athlete (daily intense exercise) | 1.9 |

Thus, assuming that the woman in the example above is active, her TDEE can be estimated as:

TDEE = 1224×1.55 = 1897.2

This number means that on average, she can consume 1897.2 calories a day and maintain weight. Consuming more will typically result in weight gain, while consuming less will typically result in weight loss.