.calorie-calculator-widget {
font-family: sans-serif;
border: 1px solid #ccc;
padding: 20px;
border-radius: 8px;
max-width: 400px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calorie-calculator-widget h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
.form-group {
margin-bottom: 15px;
}
.form-group label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.form-group input[type="number"],
.form-group select {
width: calc(100% – 12px);
padding: 8px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box;
}
.form-group button {
background-color: #4CAF50;
color: white;
padding: 10px 15px;
border: none;
border-radius: 4px;
cursor: pointer;
width: 100%;
font-size: 16px;
}
.form-group button:hover {
background-color: #45a049;
}
.calorie-result {
margin-top: 20px;
text-align: center;
font-size: 18px;
font-weight: bold;
color: #333;
}
function calculateCalories() {
var age = parseFloat(document.getElementById("age").value);
var weightKg = parseFloat(document.getElementById("weightKg").value);
var heightCm = parseFloat(document.getElementById("heightCm").value);
var heartRate = parseFloat(document.getElementById("heartRate").value);
var durationMinutes = parseFloat(document.getElementById("durationMinutes").value);
var gender = document.getElementById("gender").value;
var caloriesBurned = 0;
// Basic validation
if (isNaN(age) || isNaN(weightKg) || isNaN(heightCm) || isNaN(heartRate) || isNaN(durationMinutes) ||
age <= 0 || weightKg <= 0 || heightCm <= 0 || heartRate <= 0 || durationMinutes <= 0) {
document.getElementById("result").innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// MET values for different activities (simplified, heart rate influences this)
// These are general MET values. A more precise calculator would use a formula that
// directly links heart rate to intensity and then to METs or direct calorie expenditure.
// For a simple approximation using heart rate, we can infer intensity.
// This is a VERY simplified model. Real-world calorie calculators using heart rate
// often rely on more complex formulas like the one by 'Estela' or based on VO2 max.
// Simplified approach: assume a higher heart rate means higher intensity
// We'll use a formula that's a blend of BMR and activity intensity.
// A common approach is to estimate BMR (Basal Metabolic Rate) and then
// add calories burned during activity based on METs, which we'll approximate from heart rate.
// 1. Estimate BMR using Mifflin-St Jeor Equation
var bmr;
if (gender === "male") {
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else { // female
bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
// 2. Estimate Metabolic Equivalents (METs) from Heart Rate
// This is a rough approximation. A healthy person's Max Heart Rate is approx 220-age.
// We can map heart rate to % of Max Heart Rate for intensity.
var maxHeartRate = 220 – age;
var heartRatePercentage = (heartRate / maxHeartRate) * 100;
var mets;
if (heartRatePercentage < 50) {
mets = 3.0; // Light activity (e.g., walking slowly)
} else if (heartRatePercentage < 60) {
mets = 3.5; // Light to Moderate (e.g., brisk walking)
} else if (heartRatePercentage < 70) {
mets = 5.0; // Moderate (e.g., jogging)
} else if (heartRatePercentage < 80) {
mets = 7.0; // Vigorous (e.g., running)
} else {
mets = 9.0; // Very Vigorous (e.g., high-intensity interval training)
}
// 3. Calculate calories burned during exercise
// Formula: Calories Burned per Minute = (METs * 3.5 * weightKg) / 200
var caloriesPerMinute = (mets * 3.5 * weightKg) / 200;
caloriesBurned = caloriesPerMinute * durationMinutes;
// This calculation estimates calories burned *during* the activity.
// It does NOT include BMR for the duration of the activity.
// If you wanted total calories expended (including BMR for that time),
// you would add (bmr / 24 / 60) * durationMinutes.
// For simplicity, we'll present calories burned *from exercise*.
document.getElementById("result").innerHTML = "Estimated Calories Burned: " + caloriesBurned.toFixed(0) + " kcal";
}
Understanding Calorie Burn with Heart Rate
Your heart rate is a direct indicator of how hard your body is working during physical activity. By monitoring your heart rate, you can get a more personalized estimate of the calories you're burning. This is because different activities, even if they seem similar, can elevate your heart rate to different levels based on your fitness, intensity, and individual physiology.
The calculator above uses a common approach that combines your personal statistics (age, weight, height, gender) with your average heart rate during an exercise session and its duration. Here's a simplified breakdown of how it works:
Basal Metabolic Rate (BMR)
First, your Basal Metabolic Rate (BMR) is estimated. This is the number of calories your body burns at rest to maintain basic functions like breathing, circulation, and cell production. We use the Mifflin-St Jeor equation, which is considered one of the most accurate formulas for estimating BMR based on age, gender, weight, and height.
Activity Intensity (METs)
Next, your average heart rate during the exercise session is used to estimate the intensity of your workout. We compare your heart rate to your estimated maximum heart rate (approximately 220 minus your age) to gauge the percentage of effort you're exerting. This percentage is then used to assign a Metabolic Equivalent of Task (MET) value. METs represent the ratio of your working metabolic rate relative to your resting metabolic rate. Higher MET values signify more intense activities.
Calculating Calories Burned
Finally, the estimated MET value, your weight, and the duration of your activity are plugged into a formula to calculate the approximate calories burned during that specific exercise period. The formula essentially determines how many calories your body burns per minute based on the intensity (METs), your body mass, and then multiplies it by the total minutes you were active.
Example Calculation:
Let's consider Sarah, a 30-year-old female who weighs 65 kg and is 165 cm tall. She goes for a 45-minute run where her average heart rate is 145 bpm.
- Age: 30 years
- Weight: 65 kg
- Height: 165 cm
- Gender: Female
- Average Heart Rate: 145 bpm
- Duration: 45 minutes
Her estimated maximum heart rate is 220 – 30 = 190 bpm.
Her heart rate percentage of max is (145 / 190) * 100 ≈ 76.3%, which falls into the 'Vigorous' category, likely assigned a MET value of around 7.0.
Using the formula:
Calories per minute ≈ (7.0 METs * 3.5 * 65 kg) / 200 ≈ 7.94 kcal/minute.
Total Calories Burned ≈ 7.94 kcal/minute * 45 minutes ≈ 357 kcal.
Disclaimer: This calculator provides an estimation. Actual calorie burn can vary significantly due to individual metabolism, fitness levels, environmental factors, and the specific accuracy of heart rate monitoring devices. For precise physiological data, consult with a healthcare professional or certified exercise physiologist.