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How MET Values Turn Activity Into a Calorie Number
Every activity you do, from folding laundry to sprinting up a hill, has an energy cost that scientists have measured and standardized into something called a MET value — Metabolic Equivalent of Task. One MET is defined as the energy you burn just sitting still, roughly 1 kcal per kilogram of body weight per hour. An activity with a MET of 8, like HIIT training, burns about eight times that resting rate. This calculator uses MET values because they let you compare wildly different activities — swimming laps versus jump rope versus a yoga session — on one consistent scale, using numbers pulled from the Compendium of Physical Activities, the standard research reference exercise scientists use for this exact purpose.
The Formula Behind the Estimate
The math is straightforward once you have a MET value: calories = (MET × 3.5 × weight in kg ÷ 200) × duration in minutes. The 3.5 and 200 constants come from converting MET units into an actual oxygen-consumption-based energy expenditure per minute, which is where the "3.5 mL of oxygen per kg per minute per MET" physiological baseline gets folded in. Your weight is the other key variable — a heavier body requires more energy to move through the same activity at the same pace, which is why two people jogging side by side for 30 minutes can burn noticeably different calorie totals. Duration scales the result linearly, so doubling your time roughly doubles the calories burned, all else equal.
Picking the Right Activity and Reading Your Result
The activity list covers 15 common options spanning a wide intensity range, from restorative work like yoga and Pilates (MET 2.5-3.0) up to high-output efforts like jump rope and HIIT (MET 8.0-11.0). Pick whichever option most closely matches your actual pace and effort — walking at 3.5 mph is a brisk, purposeful pace, not a casual stroll, and running at 6 mph is a moderate jog, not a sprint. If your effort is meaningfully harder or easier than the pace implied by the listed activity, your real burn will be higher or lower than the estimate. Once you have your number, I'd use it as a planning input rather than a precise ledger entry — it's genuinely useful for comparing activities, structuring a workout week, or getting a rough sense of how a session fits into your daily calorie targets alongside a TDEE or calorie deficit calculation.
What This Estimate Can't Capture
MET-based calculations are population averages, not a direct measurement of your individual metabolism during that specific session. Your actual burn depends on factors this formula doesn't see: your fitness level (trained athletes are often more efficient and may burn slightly less doing the same work), muscle mass, terrain and incline, ambient temperature, and how consistently you held the pace throughout the session. Wearable heart-rate monitors can get closer to a personalized number but still carry their own margin of error. Treat the result here as a solid, research-grounded ballpark — good enough to compare activities and plan your week, but not precise enough to build a fragile calorie-in-calorie-out ledger around a single workout.
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