Basal Metabolic Rate (BMR) Calculator (Metric)
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic, life-sustaining functions at rest. This includes breathing, circulation, cell production, nutrient processing, protein synthesis, and ion transport. Your BMR accounts for the majority of your daily calorie expenditure, typically around 60-75%.
Understanding your BMR is crucial for weight management and overall health. It helps you determine the baseline calorie intake required to maintain your current weight. If you aim to lose weight, you'll need to consume fewer calories than your BMR (plus your activity level). If you aim to gain weight, you'll need to consume more.
Several factors influence your BMR, including:
- Age: BMR generally decreases with age.
- Sex: Men typically have a higher BMR than women due to a higher muscle mass.
- Body Composition: Muscle tissue burns more calories at rest than fat tissue.
- Body Size: Larger individuals generally have a higher BMR.
- Hormone Levels: Thyroid hormones, in particular, play a significant role.
- Genetics: Individual genetic makeup can influence metabolic rate.
How to Calculate Your BMR
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
This calculator uses the Mifflin-St Jeor Equation to provide an estimate of your Basal Metabolic Rate.
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function calculateBMR() {
var gender = document.getElementById("gender").value;
var weightKg = document.getElementById("weightKg").value;
var heightCm = document.getElementById("heightCm").value;
var ageYears = document.getElementById("ageYears").value;
var weight = parseFloat(weightKg);
var height = parseFloat(heightCm);
var age = parseFloat(ageYears);
var bmr = 0;
var resultDiv = document.getElementById("result");
if (isNaN(weight) || weight <= 0 ||
isNaN(height) || height <= 0 ||
isNaN(age) || age <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
if (gender === "male") {
bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5;
} else if (gender === "female") {
bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161;
} else {
resultDiv.innerHTML = "Please select a gender.";
return;
}
resultDiv.innerHTML = "Your estimated Basal Metabolic Rate (BMR) is: " + bmr.toFixed(2) + " calories per day.";
}