Learning how to calculate calories burned starts with a real formula exercise scientists actually use — and understanding why the number on your fitness tracker might be significantly less reliable than it looks.
Table of Contents
Quick Summary
- The standard formula: Calories burned per minute = (MET × 3.5 × your weight in kg) ÷ 200 — MET stands for “metabolic equivalent,” a measure of how intense an activity is relative to resting.
- A Stanford study testing 7 popular wrist-worn fitness trackers found none of them measured calorie burn accurately — even the best-performing device was off by 27%, and the worst was off by 93%.
- Interestingly, the same devices measured heart rate quite accurately (within 5% error) — the calorie estimate specifically is where the real inaccuracy lives.
- Trackers consistently overestimate, not just randomly miss — worth knowing if you’re using that number to justify extra food.
- The manual MET formula has its own limitations too (it uses population averages, not your individual fitness level) — but at least you know exactly where the number comes from.
The MET Formula: How to Calculate Calories Burned Manually
The formula exercise scientists actually use:
Calories burned per minute = (MET value × 3.5 × your weight in kg) ÷ 200
Here’s a worked example: if you weigh 68kg and you’re running at a pace with a MET value of 11.5 (roughly 7mph), the calculation looks like this:
11.5 × 3.5 × 68 ÷ 200 = 13.69 calories per minute
Running for 30 minutes at that pace would burn roughly 410 calories.
Why Your Fitness Tracker’s Number Might Be Wrong
This is the part most guides skip entirely. A landmark Stanford study tested seven popular wrist-worn devices (including Apple Watch and Fitbit models) against gold-standard lab equipment that measures actual oxygen consumption. The devices performed well for heart rate — most were within 5% of the accurate reading.
Calorie burn estimates told a very different story. Not a single device came close to accurate — the best performer was still off by an average of 27%, and the worst was off by 93%. If your watch says you burned 500 calories, the real number could genuinely be anywhere from roughly 350 to 650.
The practical takeaway: your tracker’s heart rate is probably trustworthy. Its calorie number is more of a rough estimate than a precise measurement — worth keeping in mind before using it to justify eating back exactly what you “burned.”
Common MET Values for Popular Activities
- Walking (moderate pace): MET 3.5
- Cycling (moderate effort): MET 8.0
- Running (6mph/10-min mile): MET 9.8
- Running (7mph/8.5-min mile): MET 11.5
- Strength training (general): MET 6.0
- Swimming (moderate effort): MET 7.0
Common Mistakes to Avoid
- Treating your tracker’s calorie number as exact. As the research shows, it’s a rough estimate at best, not a precise measurement.
- Eating back every calorie your tracker claims you burned. Given the overestimation bias, this can quietly undermine a calorie deficit.
- Ignoring the MET formula entirely. It has its own limitations, but at least the math is transparent and traceable, unlike a proprietary tracker algorithm.
- Comparing your numbers directly to someone else’s tracker. Different devices and different people can show meaningfully different results for the same activity.
Learning how to calculate calories burned is really about understanding that no single method — manual formula or wearable device — gives you a perfectly exact number. The MET formula at least shows its work; your tracker mostly doesn’t. If you’re using this to plan a deficit, our calorie deficit guide and protein intake calculator round out the rest of the picture.
Disclaimer & Affiliate Disclosure
This article is for informational purposes only and should not be taken as medical advice. Always consult with a qualified healthcare provider or certified fitness professional before starting or changing your diet or exercise routine. This article may also contain affiliate links. If you purchase through these links, we may earn a small commission at no extra cost to you.
