The Calories Burned Calculator uses the MET framework to translate your body weight, activity choice, duration, and intensity into a concrete calorie and fat-burn estimate — helping you plan workouts, track deficits, and compare activities side by side.
How the MET Formula Works
The Metabolic Equivalent of Task (MET) is a standardized measure published by the Compendium of Physical Activities (Ainsworth et al.) that expresses how much energy an activity demands relative to sitting at rest. The formula Calories = MET × Weight (kg) × Duration (hours) applies this ratio to your body mass and session length. Because heavier individuals move more mass and therefore burn more energy per unit of time, weight is a direct multiplier in the equation. A 200 lb person running at the same speed as a 150 lb person burns roughly 33% more calories per minute. Duration scales linearly — doubling your workout time doubles calories burned, all else equal. Intensity affects the MET value chosen: vigorous running at 8 mph (MET ~11.8) burns substantially more than an easy jog at 5 mph (MET ~8.3). The calculator selects the appropriate MET from the Compendium based on your activity and intensity selection, applies your weight conversion from pounds to kilograms, and multiplies by fractional hours to produce a gross calorie estimate consistent with the method used in clinical exercise physiology research.
Inputs and Assumptions
Every input carries hidden assumptions worth understanding. Body weight is entered in pounds and converted internally to kilograms, since METs are defined per kilogram of body mass. Duration is entered in minutes and converted to decimal hours. The activity list draws MET values from the 2011 Compendium, the most widely cited reference. Intensity — light, moderate, or vigorous — maps to the lower, mid, or upper MET values listed for each activity, since most activities have a range rather than a single MET. The fat oxidation calculation applies an intensity-dependent factor: at light intensity, roughly 65% of calories come from fat; at moderate, about 55%; at vigorous, approximately 40%, as the body increasingly relies on fast-burning carbohydrates. These factors are derived from exercise physiology research and represent population averages. Individual variation in body composition, fitness level, and metabolic efficiency means your actual fuel mix may differ by 5–15 percentage points from these defaults. Treat fat-burn estimates as directional rather than precise.
When Results May Differ from Reality
MET-based calorie estimates typically fall within ±15–20% of actual energy expenditure for most people under standard conditions. Several factors can push your real burn outside this range. Fitness level matters significantly: a well-trained runner at 6 mph works at a lower percentage of their maximum capacity than a beginner at the same speed, and the trained athlete will burn slightly fewer calories because their body has become more efficient. Environmental conditions also play a role — heat, humidity, altitude, and wind resistance all affect metabolic cost but are invisible to the formula. Body composition is another variable: individuals with higher muscle mass have elevated resting metabolic rates, which raises gross burn. Wearable devices that incorporate heart rate data can produce more personalized estimates, though they introduce their own error sources. For day-to-day planning, MET calculations are accurate enough for tracking weekly calorie expenditure trends. For clinical or research-grade precision — such as planning a supervised weight-loss program — indirect calorimetry in a metabolic laboratory provides the gold standard measurement.