🏃 🏃 How to Calculate Calories Burned During Exercise

Fitness trackers, gym equipment, and online calculators estimate calories burned during exercise — but how accurate are they, and what determines the number? The answer is a concept called MET (Metabolic Equivalent of Task), which provides a standardized way to express exercise intensity and calculate calorie expenditure across any physical activity.

What is a MET?

MET stands for Metabolic Equivalent of Task. One MET is the energy your body uses at complete rest — approximately 1 calorie per kilogram of body weight per hour, or 3.5 mL of oxygen per kilogram per minute.

An activity with a MET value of 4 means you burn 4× more energy than at rest. Running at 6 mph has a MET of about 10 — you burn 10× more energy than sitting still.

• MET 1–3: Light intensity (sitting, standing, slow walking)
• MET 3–6: Moderate intensity (brisk walking, casual cycling)
• MET 6+: Vigorous intensity (running, swimming, competitive sports)

The Calorie Burn Formula

The standard MET-based calorie calculation formula, used by NASM and widely in clinical practice:

Calories burned/minute = MET × 3.5 × body weight (kg) ÷ 200

Or equivalently: Calories burned = MET × weight (kg) × time (hours)

Worked Example: Running at 7 mph

• MET for running at 7 mph = 11.5
• Body weight: 70 kg (154 lbs)
• Duration: 30 minutes (0.5 hours)
• Calories = 11.5 × 70 × 0.5 = 402.5 calories

Worked Example: Walking the Dog

• MET for walking the dog = 3.0
• Body weight: 65 kg
• Duration: 45 minutes (0.75 hours)
• Calories = 3.0 × 65 × 0.75 = 146.25 calories

MET Values for Common Activities

Why Body Weight Matters So Much

Body weight is directly proportional to calorie burn in the MET formula. A 100 kg person and a 60 kg person doing the same activity for the same duration burn very different calories:

• 60 kg person running at 5 mph for 30 min: 8.3 × 60 × 0.5 = 249 calories
• 100 kg person running at 5 mph for 30 min: 8.3 × 100 × 0.5 = 415 calories

This is why heavier people often lose weight faster initially when starting an exercise routine — every activity burns proportionally more calories for them.

How Accurate are Fitness Trackers?

Consumer fitness trackers (Fitbit, Apple Watch, Garmin) typically overestimate calorie burn by 20–70% depending on the activity. Running estimates tend to be more accurate (15–20% over) than cycling or strength training (40–70% over) because running speed and cadence can be measured more precisely.

Key reasons for inaccuracy:

• Heart rate-based estimates don't account for fitness level (a fit person burns fewer calories at the same heart rate than an unfit person)
• Wrist-based heart rate monitors are less accurate during strength training and high-intensity intervals
• Most devices add NEAT (non-exercise activity) to workout burns, double-counting some movement

Best practice: Use tracker estimates as relative comparisons (did I burn more today than yesterday?) rather than absolute numbers for diet planning.

The Physical Activity Guidelines

The 2018 Physical Activity Guidelines for Americans recommend:

• Moderate intensity: 150–300 minutes per week (METs 3–6), OR
• Vigorous intensity: 75–150 minutes per week (METs 6+), OR
• A combination of both
• Strength training: 2+ days per week, all major muscle groups

A useful target from the American Heart Association: 500 MET-minutes per week. Calculate your MET-minutes: MET value × minutes of activity. Brisk walking (3.5 MET) for 150 minutes = 525 MET-minutes — meeting the guideline.

Burning 500 Calories: Time Required by Activity

• Running at 6 mph: ~35–40 minutes
• Cycling at moderate pace: ~55–65 minutes
• Swimming (moderate): ~70–80 minutes
• Brisk walking: ~90–110 minutes
• Yoga: ~170 minutes
• Weight lifting: ~120 minutes

(Estimated for 70 kg / 154 lbs person; heavier people reach 500 calories faster)