Basal Metabolic Rate Calculator Body Fat

Your Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to perform its essential functions while at rest. These functions include breathing, circulation, cell production, nutrient processing, protein synthesis, and the functioning of the nervous system. Essentially, it's the energy your body burns just to keep you alive and functioning, even if you were to do nothing all day.

Factors that influence BMR include age, gender, body weight, height, and body composition, particularly the amount of lean body mass. Lean body mass (which includes muscle, bone, and organs) is metabolically more active than fat tissue, meaning it burns more calories at rest. Therefore, understanding your body fat percentage can give you a clearer picture of your metabolic health and calorie needs.

How BMR is Calculated

The most common formulas used to estimate BMR are the Harris-Benedict equation and the Mifflin-St Jeor equation. The Mifflin-St Jeor equation is generally considered more accurate for most individuals.

Mifflin-St Jeor Equation:

• For Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
• For Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

Lean Body Mass (LBM)

Lean Body Mass (LBM) is the total weight of your body minus the weight of your body fat. It is a crucial indicator of metabolic health because muscle tissue burns significantly more calories at rest than fat tissue. A higher LBM generally leads to a higher BMR.

LBM can be calculated using your total body weight and your body fat percentage:

LBM (kg) = Weight (kg) × (1 – (Body Fat Percentage / 100))

Using This Calculator

This calculator uses the Mifflin-St Jeor equation to estimate your BMR and also calculates your Lean Body Mass. By inputting your gender, weight, height, age, and body fat percentage, you can get a personalized estimate of your daily calorie needs at rest and understand how your body composition affects your metabolism. This information can be valuable for managing weight, improving fitness, and making informed dietary choices.

Example Calculation:

Let's consider a 35-year-old male who weighs 80 kg, is 180 cm tall, and has a body fat percentage of 22%.

Gender: Male
Weight: 80 kg
Height: 180 cm
Age: 35 years
Body Fat Percentage: 22%

BMR Calculation (Mifflin-St Jeor for Men):
BMR = (10 × 80) + (6.25 × 180) – (5 × 35) + 5
BMR = 800 + 1125 – 175 + 5
BMR = 1755 calories

Lean Body Mass Calculation:
LBM = 80 kg × (1 – (22 / 100))
LBM = 80 kg × (1 – 0.22)
LBM = 80 kg × 0.78
LBM = 62.4 kg

For this individual, the estimated BMR is 1755 calories, and their Lean Body Mass is 62.4 kg. This indicates that a significant portion of their body weight is lean mass, contributing to a higher resting metabolism.

function calculateBMR() { var gender = document.getElementById("gender").value; var weight = parseFloat(document.getElementById("weight").value); var height = parseFloat(document.getElementById("height").value); var age = parseFloat(document.getElementById("age").value); var bodyFatPercentage = parseFloat(document.getElementById("bodyFatPercentage").value); var bmr = 0; var leanBodyMass = 0; if (isNaN(weight) || isNaN(height) || isNaN(age) || isNaN(bodyFatPercentage)) { document.getElementById("bmrResult").innerHTML = "Please enter valid numbers for all fields."; document.getElementById("leanBodyMassResult").innerHTML = ""; return; } if (gender === "male") { bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5; } else { // female bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161; } if (bodyFatPercentage >= 0 && bodyFatPercentage <= 100) { leanBodyMass = weight * (1 – (bodyFatPercentage / 100)); } else { leanBodyMass = NaN; // Indicate invalid body fat percentage } document.getElementById("bmrResult").innerHTML = "Your Basal Metabolic Rate (BMR) is: " + bmr.toFixed(2) + " calories"; if (!isNaN(leanBodyMass)) { document.getElementById("leanBodyMassResult").innerHTML = "Your Lean Body Mass is: " + leanBodyMass.toFixed(2) + " kg"; } else { document.getElementById("leanBodyMassResult").innerHTML = "Invalid Body Fat Percentage entered. Cannot calculate Lean Body Mass."; } }