BMR Calculator

This guide will walk you through calculating your Basal Metabolic Rate (BMR), which is the number of calories your body burns at rest to maintain basic physiological functions. Understanding your BMR is crucial for effective weight management, whether you're aiming to lose, gain, or maintain weight, as it forms the foundation of your daily caloric needs.

The most widely accepted and accurate formula for calculating BMR is the Mifflin-St Jeor equation. This formula takes into account your sex, weight, height, and age. It's a more modern and generally preferred equation compared to older methods like the Harris-Benedict equation. The core idea is to estimate the energy expenditure required for essential bodily functions such as breathing, circulation, cell production, nutrient processing, and temperature regulation, assuming you're in a completely rested state.

Let's break down the Mifflin-St Jeor equation. First, you'll need to convert your height from feet and inches into centimeters, and your weight from pounds into kilograms, as the formula uses metric units. Height in centimeters = ((feet * 12) + inches) * 2.54 Weight in kilograms = weight in pounds * 0.453592

Once you have these conversions, the formula diverges slightly based on sex: For men, the BMR formula is: BMR = (10 * weight in kg) + (6.25 * height in cm) - (5 * age in years) + 5 For women, the BMR formula is: BMR = (10 * weight in kg) + (6.25 * height in cm) - (5 * age in years) - 161

Let's walk through a few examples to illustrate.

**Example 1: A 30-year-old male** Inputs: Age = 30, Sex = Male, Height = 5 feet 10 inches, Weight = 170 lbs

First, convert height and weight: Height in cm = ((5 * 12) + 10) * 2.54 = (60 + 10) * 2.54 = 70 * 2.54 = 177.8 cm Weight in kg = 170 * 0.453592 = 77.11 kg

Now, apply the male BMR formula: BMR = (10 * 77.11) + (6.25 * 177.8) - (5 * 30) + 5 BMR = 771.1 + 1111.25 - 150 + 5 BMR = 1737.35 calories (approximately 1737 calories)

**Example 2: A 45-year-old female** Inputs: Age = 45, Sex = Female, Height = 5 feet 4 inches, Weight = 140 lbs

First, convert height and weight: Height in cm = ((5 * 12) + 4) * 2.54 = (60 + 4) * 2.54 = 64 * 2.54 = 162.56 cm Weight in kg = 140 * 0.453592 = 63.50 kg

Now, apply the female BMR formula: BMR = (10 * 63.50) + (6.25 * 162.56) - (5 * 45) - 161 BMR = 635 + 1016 - 225 - 161 BMR = 1265 calories

**Example 3: A 25-year-old male** Inputs: Age = 25, Sex = Male, Height = 6 feet 1 inch, Weight = 200 lbs

First, convert height and weight: Height in cm = ((6 * 12) + 1) * 2.54 = (72 + 1) * 2.54 = 73 * 2.54 = 185.42 cm Weight in kg = 200 * 0.453592 = 90.72 kg

Now, apply the male BMR formula: BMR = (10 * 90.72) + (6.25 * 185.42) - (5 * 25) + 5 BMR = 907.2 + 1158.875 - 125 + 5 BMR = 1946.075 calories (approximately 1946 calories)

When calculating your BMR, a common mistake is using incorrect units. Always ensure your height is converted to centimeters and weight to kilograms before plugging them into the Mifflin-St Jeor equation. Another pitfall is confusing BMR with Total Daily Energy Expenditure (TDEE). BMR is just the baseline; TDEE includes your BMR plus the calories burned through physical activity. To get your TDEE, you would multiply your BMR by an activity factor (e.g., 1.2 for sedentary, 1.375 for lightly active, etc.). Also, remember that BMR is an estimate; individual metabolic rates can vary due to factors like genetics, body composition (muscle mass burns more calories than fat), and hormonal levels. It's a useful starting point, but not an absolute truth.

While you can manually perform these calculations, using a dedicated BMR calculator is often more convenient and reduces the chance of arithmetic errors, especially with the unit conversions. It's particularly helpful when you want to quickly compare BMRs under different scenarios or for multiple individuals. For a precise and quick result, a calculator is the way to go.

The Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to perform basic, life-sustaining functions while at rest. These essential functions include breathing, circulation, cell production, nutrient processing, and temperature regulation. Understanding your BMR is a foundational step in managing your weight, whether you're aiming to lose, gain, or maintain it, as it provides the baseline caloric expenditure before accounting for any physical activity.

The ProCalc.ai BMR Calculator utilizes the Mifflin-St Jeor equation, which is widely recognized as one of the most accurate BMR prediction formulas. This equation was developed in 1990 and is preferred by many health professionals over older formulas like the Harris-Benedict equation due to its improved accuracy across diverse populations.

The core formulas for calculating BMR using the Mifflin-St Jeor equation are:

For males:
BMR = (10 * weight in kg) + (6.25 * height in cm) - (5 * age in years) + 5

For females:
BMR = (10 * weight in kg) + (6.25 * height in cm) - (5 * age in years) - 161

Let's break down each variable and the necessary unit conversions. The calculator takes your weight in pounds (lbs), height in feet and inches, and age in years. For the formula, these need to be converted to kilograms (kg) and centimeters (cm) respectively.

First, your weight in pounds is converted to kilograms. One pound is approximately 0.453592 kilograms. So, if you weigh 170 lbs, the calculation would be 170 lbs * 0.453592 kg/lb = 77.11 kg.

Next, your height, provided in feet and inches, is converted to centimeters. There are 12 inches in a foot, and one inch is approximately 2.54 centimeters. For example, if you are 5 feet 10 inches tall:
First, convert feet to inches: 5 feet * 12 inches/foot = 60 inches.
Add the remaining inches: 60 inches + 10 inches = 70 inches.
Finally, convert total inches to centimeters: 70 inches * 2.54 cm/inch = 177.8 cm.

Your age is used directly in years.

Once these conversions are made, the values are plugged into the appropriate formula based on your sex. For instance, for a 30-year-old male weighing 170 lbs (77.11 kg) and standing 5 feet 10 inches (177.8 cm) tall, the calculation would be:
BMR = (10 * 77.11) + (6.25 * 177.8) - (5 * 30) + 5
BMR = 771.1 + 1111.25 - 150 + 5
BMR = 1737.35 calories

For a 30-year-old female with the same weight and height:
BMR = (10 * 77.11) + (6.25 * 177.8) - (5 * 30) - 161
BMR = 771.1 + 1111.25 - 150 - 161
BMR = 1571.35 calories

It's important to note that BMR formulas, including Mifflin-St Jeor, are estimates. They do not account for individual variations in body composition, such as muscle mass versus fat mass, which can significantly impact metabolic rate. Highly muscular individuals may have a higher BMR than predicted, while those with a higher percentage of body fat might have a slightly lower BMR. Additionally, factors like illness, pregnancy, breastfeeding, and extreme environmental temperatures can temporarily alter your metabolic rate. While the Mifflin-St Jeor equation is generally robust, it's always a good idea to consider these individual nuances and consult with a healthcare professional or registered dietitian for personalized advice.