Calculating Basal Metabolic Rate Formula

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Basal Metabolic Rate (BMR) Calculator

Male Female
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 bmr = 0; if (isNaN(weight) || isNaN(height) || isNaN(age)) { document.getElementById("result").innerHTML = "Please enter valid numbers for all fields."; return; } if (gender === "male") { bmr = 88.362 + (13.397 * weight) + (4.799 * height) – (5.677 * age); } else { // female bmr = 447.593 + (9.247 * weight) + (3.098 * height) – (4.330 * age); } document.getElementById("result").innerHTML = "Your estimated Basal Metabolic Rate (BMR) is: " + bmr.toFixed(2) + " calories/day"; } .bmr-calculator { font-family: sans-serif; border: 1px solid #ccc; padding: 20px; border-radius: 8px; max-width: 400px; margin: 20px auto; background-color: #f9f9f9; } .bmr-calculator h2 { text-align: center; margin-bottom: 20px; color: #333; } .bmr-calculator .inputs { display: grid; gap: 15px; } .bmr-calculator .form-group { display: flex; flex-direction: column; } .bmr-calculator label { margin-bottom: 5px; font-weight: bold; color: #555; } .bmr-calculator input[type="number"], .bmr-calculator select { padding: 10px; border: 1px solid #ccc; border-radius: 4px; font-size: 1rem; } .bmr-calculator button { padding: 12px 20px; background-color: #007bff; color: white; border: none; border-radius: 4px; cursor: pointer; font-size: 1.1rem; transition: background-color 0.3s ease; } .bmr-calculator button:hover { background-color: #0056b3; } .bmr-calculator .result { margin-top: 25px; padding: 15px; background-color: #e7f3ff; border: 1px solid #b3d4ff; border-radius: 4px; text-align: center; font-size: 1.1rem; color: #0056b3; }

Understanding Basal Metabolic Rate (BMR)

Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to perform basic, life-sustaining functions at rest. These functions include breathing, circulation, cell production, nutrient processing, and protein synthesis. Essentially, it's the energy your body burns just to keep you alive if you were to do absolutely nothing all day.

Your BMR accounts for a significant portion of your daily calorie expenditure, typically around 60-75% of your total daily energy needs. Factors influencing your BMR include:

  • Age: BMR generally decreases with age.
  • Gender: Men tend to have a higher BMR than women due to generally higher muscle mass.
  • Body Composition: Muscle tissue burns more calories at rest than fat tissue. Therefore, individuals with more lean muscle mass have a higher BMR.
  • Body Size and Shape: Larger individuals generally have a higher BMR.
  • Genetics: Your inherited traits can play a role in your metabolic rate.
  • Hormones: Hormonal imbalances can affect BMR.
  • Body Temperature: A fever can significantly increase BMR.
  • Environmental Temperature: Extreme cold or heat can increase BMR as the body works to maintain its core temperature.

The Mifflin-St Jeor Equation

The calculator above uses the Mifflin-St Jeor equation, which is widely considered one of the most accurate formulas for estimating BMR.

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

While the Mifflin-St Jeor equation is common, another well-known formula is the Harris-Benedict equation, which has been revised over time. The key takeaway is that these are estimations, and individual metabolisms can vary.

Why is BMR Important?

Understanding your BMR is crucial for weight management and overall health. It serves as a baseline for calculating your Total Daily Energy Expenditure (TDEE). To find your TDEE, you multiply your BMR by an activity factor that reflects your daily physical activity level. Knowing your BMR helps you:

  • Weight Loss: To lose weight, you need to consume fewer calories than your TDEE.
  • Weight Gain: To gain weight, you need to consume more calories than your TDEE.
  • Weight Maintenance: To maintain your current weight, your calorie intake should roughly equal your TDEE.

This calculator provides an estimate of your BMR. For personalized advice on nutrition and exercise, it's always recommended to consult with a healthcare professional or a registered dietitian.

Example Calculation:

Let's calculate the BMR for a 30-year-old female who weighs 65 kg and is 165 cm tall.

Using the Mifflin-St Jeor equation for women:
BMR = (10 × 65) + (6.25 × 165) – (5 × 30) – 161
BMR = 650 + 1031.25 – 150 – 161
BMR = 1370.25 calories/day

So, this individual needs approximately 1370.25 calories per day just to maintain her basic bodily functions at rest. Her total daily calorie needs would be higher depending on her activity level.

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