Calories
Calories measure energy used by the body during exercise. Learn how calorie burn is calculated, factors affecting energy expenditure, and how to use calorie data for training and nutrition.
Quick Answer
Calories — A calorie (technically kilocalorie or kcal) is a unit of energy. In exercise, calories measure how much energy your body burns during physical activity. The number of calories burned depends on activity type, intensity, duration, and body weight.
What is a Calorie?
A calorie is the energy needed to raise 1 gram of water by 1°C. In nutrition:
| Term | Definition |
|---|---|
| Calorie (cal) | Small calorie (scientific) |
| Kilocalorie (kcal) | 1,000 calories = food "Calorie" |
| Calorie (food) | Actually means kilocalorie |
When we say "burned 500 calories," we mean 500 kilocalories.
How Calories are Burned
Components of Daily Energy Expenditure
| Component | % of Daily Total |
|---|---|
| BMR (Basal Metabolic Rate) | 60-75% |
| TEF (Thermic Effect of Food) | 10% |
| Activity (NEAT + Exercise) | 15-30% |
Exercise Calorie Calculation
Basic formula using MET values:
Calories = MET × weight (kg) × time (hours)
Example (70kg, 8 MET activity, 1 hour):
Calories = 8 × 70 × 1 = 560 calories
Calories Burned by Activity
Running
| Pace | Calories/Hour (70kg) |
|---|---|
| 10:00/mile (9.6 km/h) | 600 |
| 8:00/mile (12 km/h) | 750 |
| 7:00/mile (13.7 km/h) | 850 |
| 6:00/mile (16 km/h) | 1,000 |
Use our Running Calorie Calculator.
Cycling
| Intensity | Calories/Hour (70kg) |
|---|---|
| Leisurely (< 16 km/h) | 280 |
| Moderate (16-19 km/h) | 420 |
| Vigorous (19-24 km/h) | 560 |
| Racing (> 24 km/h) | 700+ |
Use our Cycling Calorie Calculator.
Other Activities
| Activity | Calories/Hour (70kg) |
|---|---|
| Walking | 250-350 |
| Swimming | 400-700 |
| Rowing | 400-800 |
| Elliptical | 450-650 |
| HIIT | 500-900 |
| Jump rope | 600-900 |
Factors Affecting Calorie Burn
Body Weight
Heavier people burn more calories for the same activity:
| Weight | Calories (1 hour running) |
|---|---|
| 55kg | 500 |
| 70kg | 640 |
| 85kg | 780 |
| 100kg | 920 |
Intensity
Higher intensity = more calories per minute:
Duration
Longer workouts burn more total calories:
| Duration | Moderate Run Calories (70kg) |
|---|---|
| 30 min | 320 |
| 60 min | 640 |
| 90 min | 960 |
| 120 min | 1,280 |
Efficiency
Trained athletes may burn fewer calories at the same pace due to improved economy. However, they typically train at higher intensities.
Calorie Tracking Accuracy
Device Accuracy
| Device | Typical Accuracy |
|---|---|
| Chest HR monitor | ±10-15% |
| Wrist HR monitor | ±15-25% |
| Power meter (cycling) | ±5-10% |
| Machine displays | ±20-30% |
| MET-based calculators | ±15-20% |
Why Estimates Vary
| Factor | Impact |
|---|---|
| Individual metabolism | ±10-20% |
| Efficiency differences | ±10-15% |
| Environmental conditions | ±5-10% |
| Device limitations | ±10-20% |
Calories for Weight Management
Calorie Balance
| State | Calorie Balance |
|---|---|
| Weight loss | Calories in < Calories out |
| Maintenance | Calories in = Calories out |
| Weight gain | Calories in > Calories out |
Exercise and Weight Loss
| Reality | Detail |
|---|---|
| Exercise helps but... | Diet typically has bigger impact |
| Calorie burn | Often overestimated |
| Compensation | May eat more after exercise |
| Best approach | Combine exercise + nutrition |
Read: Cycling vs Running Weight Loss.
Calories for Performance
During Exercise
For long efforts, replace some calories:
| Duration | Calorie Intake |
|---|---|
| < 60 min | Usually none needed |
| 60-90 min | 100-200 calories |
| 90+ min | 200-300 cal/hour |
| Endurance events | 300-400 cal/hour |
Recovery
| Timing | Goal |
|---|---|
| Post-workout | Replace glycogen |
| Target | 0.5-1g carbs/kg within 2 hours |
| Example (70kg) | 35-70g carbs (~140-280 cal) |
Calculating Your Needs
Daily Calorie Needs
| Activity Level | Multiplier |
|---|---|
| Sedentary | BMR × 1.2 |
| Light activity | BMR × 1.375 |
| Moderate activity | BMR × 1.55 |
| Very active | BMR × 1.725 |
| Athlete | BMR × 1.9-2.2 |
Training Day Adjustments
| Training Volume | Additional Calories |
|---|---|
| 1-hour easy | +300-500 |
| 1-hour hard | +500-800 |
| 2-hour moderate | +800-1,200 |
| 3+ hours | +1,200-2,000 |
Common Questions
Are all calories equal?
Energetically yes, but nutritionally no:
- Carbs: Best for exercise performance
- Protein: Essential for recovery
- Fat: Important for health, slower fuel
How accurate are exercise machines?
Generally overestimate by 20-30%. Use them for relative comparison, not absolute values.
Should I eat back exercise calories?
For weight loss: Eat back 50-75% to avoid over-restriction. For performance: Fuel adequately to support training.
Why do I burn fewer calories as I get fitter?
Improved efficiency means less energy wasted. However, you can also train harder and longer, often burning more total calories.