Understanding the energy you expend during physical activity is crucial for weight management, athletic training, and general health tracking. While smartwatches provide estimates, you can calculate calories burned manually using the MET (Metabolic Equivalent of Task) formula.
The Science: What is a MET?
A Metabolic Equivalent of Task (MET) is a unit that estimates the amount of energy the body uses during physical activity compared to resting metabolism. One MET is defined as the energy cost of sitting quietly, which is approximately 3.5 milliliters of oxygen consumed per kilogram of body weight per minute.
The Calories Burned Formula
To calculate the calories burned per activity, the standard scientific formula is:
Calories Burned = (MET × 3.5 × Weight in kg / 200) × Duration in minutes
Common Activities and Their MET Values
Activity
Intensity
MET Value
Yoga (Hatha)
Light
2.5
Walking (3.5 mph)
Moderate
4.3
Tennis (Doubles)
Moderate
5.0
High-Intensity Interval Training (HIIT)
Vigorous
8.0
Running (8 mph)
Very Vigorous
11.8
Factors That Influence Calorie Burn
While the calculator provides a solid estimate, several biological factors can change the actual number of calories you burn:
Body Composition: Muscle tissue is more metabolically active than fat tissue. Individuals with higher muscle mass burn more calories even at rest.
Age: As we age, our metabolic rate generally slows down due to the loss of muscle tissue and hormonal changes.
Environmental Temperature: Working out in extreme heat or cold forces the body to work harder to maintain its core temperature, increasing calorie expenditure.
Fitness Level: As you become more fit, your body becomes more efficient. You may actually burn fewer calories performing the same exercise as you did when you were less fit.
Practical Example
If a person weighs 80 kg and goes for a 30-minute brisk walk (MET value of 3.5), the calculation would be:
(3.5 MET × 3.5 × 80 kg) / 200 = 4.9 calories per minute.
4.9 calories × 30 minutes = 147 total calories burned.
function calculateCalories() {
var weight = parseFloat(document.getElementById('cbWeight').value);
var duration = parseFloat(document.getElementById('cbDuration').value);
var metValue = parseFloat(document.getElementById('cbActivity').value);
var resultDiv = document.getElementById('cbResult');
var valueDisplay = document.getElementById('cbValue');
// Validation
if (isNaN(weight) || weight <= 0) {
alert("Please enter a valid weight in kilograms.");
return;
}
if (isNaN(duration) || duration <= 0) {
alert("Please enter a valid duration in minutes.");
return;
}
// Formula: (MET * 3.5 * weight) / 200 = Calories per minute
// Total = (Calories per minute) * duration
var caloriesPerMinute = (metValue * 3.5 * weight) / 200;
var totalBurned = caloriesPerMinute * duration;
// Display Result
valueDisplay.innerHTML = Math.round(totalBurned) + " kcal";
resultDiv.style.display = "block";
// Scroll to result smoothly
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}