Basal Metabolic Rate (BMR) Calculator
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions, such as breathing, circulation, and cell production, while at rest. It's essentially the minimum energy your body requires to keep you alive. Understanding your BMR can be a foundational step in managing your weight, designing a fitness plan, or simply understanding your body's energy needs.
Several factors influence your BMR, including age, sex, weight, height, and body composition (muscle mass vs. fat mass). The most commonly used formulas to estimate BMR are the Harris-Benedict Equation (revised in 1984) and the Mifflin-St Jeor Equation (considered more accurate by many researchers).
Understanding BMR Calculations
The calculator above typically uses the Mifflin-St Jeor Equation, which is widely accepted as one of the most accurate BMR estimation formulas:
- 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
The Harris-Benedict Equation (revised) is another option:
- For Men: BMR = (13.397 × weight in kg) + (4.799 × height in cm) – (5.677 × age in years) + 88.362
- For Women: BMR = (9.247 × weight in kg) + (3.098 × height in cm) – (4.330 × age in years) + 447.593
This calculator focuses on the Mifflin-St Jeor equation for its accuracy. Remember that BMR is just an estimate. Your actual daily calorie needs will also depend on your activity level (this is often referred to as Total Daily Energy Expenditure or TDEE).
function calculateBMR() { var gender = document.getElementById("gender").value; var age = parseFloat(document.getElementById("age").value); var weightKg = parseFloat(document.getElementById("weight").value); var heightCm = parseFloat(document.getElementById("heightCm").value); var heightIn = parseFloat(document.getElementById("heightIn").value); var bmr = 0; // Validate inputs if (isNaN(age) || isNaN(weightKg) || isNaN(heightCm) || isNaN(heightIn) || age <= 0 || weightKg <= 0 || heightCm <= 0 || heightIn <= 0) { document.getElementById("result").innerHTML = "Please enter valid positive numbers for all fields."; return; } // Ensure consistency between cm and inches – use cm for calculation // Convert inches to cm if needed, but prioritize direct cm input // For simplicity here, we'll assume user enters either valid cm OR valid inches, and use the cm value. // A more robust calculator might handle conversions more explicitly or guide user. if (gender === "male") { bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5; } else { // female bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161; } document.getElementById("result").innerHTML = "Your estimated Basal Metabolic Rate (BMR) is: " + bmr.toFixed(2) + " calories per day"; }