How Does the Apple Watch Calculate Calories for Workouts?

Okay, maybe I’m a bit obsessive, but when I spend $400 on a device, I expect it to perform as advertised. Early today, I showed that the Apple Watch confuses miles and kilometers, and doesn’t count distances for indoor walks very well. In the past, I’ve also pointed out how there are problems with the heart rate sensor, and that the device’s resting calories are from the realm of science fiction.

After a friend read the article about miles and kilometers today, he said, “78 calories? That’s weird.”

Apple watch miles kilometers

I had never actually considered whether the calorie counts were correct or not, though I’d heard some people report very odd numbers. So I went to an online calculator, entered my weight, the grade of my treadmill (measured with the Compass app on the iPhone), the distance the treadmill recorded, and the time. It told me:

You burned an estimated 230 calories.

Now, that calculator is counting gross calories, or what the Activty app displays as Total calories (Active plus Resting). But there’s still a huge discrepancy: 144 for the Apple Watch, 230 for the calculator.

The same website also has a calculator that uses your heart rate. Since the Apple Watch records this – albeit not very accurately – I went back to a 20-minute outdoor walk I did last week. I entered the time, the average heart rate, and the rest of the information, and the calculautor told me:

At a heartrate of 109 bpm, or 64% of your estimated maximum heartrate (170 bpm), your calorie burn is an estimated 646 calories per hour. In 19 minutes and 43 seconds you will burn approximately 212 calories.

The Activity app says I burned 83 active calories, and a total of 128 calories.

Hmm…

It’s worth noting that the type of workout you choose seems to affect the calorie count. If I walk on my treadmill, I can choose either an Indoor Walk workout or an Other workout. Here are the calorie counts for both kinds of workouts, for 30-minute walks at 3.5 mph in the past few days:

Indoor Walk: 91
Other: 179

I think that Apple needs to do some work on this whole fitness tracker thing. It’s hard to take any of this seriously now.

34 thoughts on “How Does the Apple Watch Calculate Calories for Workouts?

  1. Something I’d be very interested to see: For the same workout, wear a traditional heart rate monitor (one of the ones that require a strap around the chest) AND an Apple Watch. Then compare results.

    I use a Polar HRM that generally gets my heart rate exactly right (I know this because every now and then I physically check my heart rate using my pulse). From that it calculates calories burned using my weight, heart rate, resting heart rate, age and gender.

    I’m only willing to purchase an Apple Watch if its accuracy and reliability is as good as, or better than, my Polar HRM.

    Having said that, there are a great many different formulas used to calculate calories burned — it’s an extremely inexact science; some would say it’s not a science at all. So I’m willing to give Apple a bit of latitude when it comes to calorie count calculations … but not when it comes to getting the actual heart rate right.

  2. Something I’d be very interested to see: For the same workout, wear a traditional heart rate monitor (one of the ones that require a strap around the chest) AND an Apple Watch. Then compare results.

    I use a Polar HRM that generally gets my heart rate exactly right (I know this because every now and then I physically check my heart rate using my pulse). From that it calculates calories burned using my weight, heart rate, resting heart rate, age and gender.

    I’m only willing to purchase an Apple Watch if its accuracy and reliability is as good as, or better than, my Polar HRM.

    Having said that, there are a great many different formulas used to calculate calories burned — it’s an extremely inexact science; some would say it’s not a science at all. So I’m willing to give Apple a bit of latitude when it comes to calorie count calculations … but not when it comes to getting the actual heart rate right.

  3. I think this is related to the problem with distance on indoor walks/runs. If, as you suggested earlier, the Watch is confusing miles and kilometers, which I think mine is doing too, then its distance calculations will be off by a factor of 2.2. Assuming its calorie estimates are based on distance that will then be off by the same factor. I note that other activates, such as outdoor walk/run or on the elliptical, the calories are fine.

    BTW, I am on the phone with Apple Support as I type this. They haven’t got a clue.

  4. I think this is related to the problem with distance on indoor walks/runs. If, as you suggested earlier, the Watch is confusing miles and kilometers, which I think mine is doing too, then its distance calculations will be off by a factor of 2.2. Assuming its calorie estimates are based on distance that will then be off by the same factor. I note that other activates, such as outdoor walk/run or on the elliptical, the calories are fine.

    BTW, I am on the phone with Apple Support as I type this. They haven’t got a clue.

  5. If walking for 20 minutes burned 212 calories we’d all be a lot thinner! Apple’s measurement seems a lot more realistic. Back when I tracked only distance by memorizing where I walked and then later using Map My Run, I would use 80 calories per mile to give me a sense of how many active calories I burned. Now that I have an Apple Watch, it seems quite realistic. For example, it shows 210 active calories for a 2.86 mile walk yesterday during which time my average heart rate was 111. Maybe that website you’re using has a problem and not Apple Watch. I think you need to jump much deeper into the science, which I suspect Apple has given the reliable-looking data I’m getting.

    • The Fitbi app lets you record walks and runs. I’ve only done it a few times, but for a 22 minute walk at roughly the same pace, it records 110 cal. Extrapolate that to a half hour, and it’s about 150 cal. That is still very far from what Apple is suggesting. I know there were several ways of calculating calories, and none of them are exact, but everyone I checked shows much higher numbers than Apple.

      • Your comparison is ridiculous…you’re just assuming that the FitBit is correct, and the Watch MUST be wrong because they 2 readings aren’t the same. The other possibility is that the FitBit is wrong, even if other trackers match it. Or yet a third possibility is what others have mentioned – calorie counting is a pseudo-science and nobody really knows what’s actually going on. Even the word “calorie” is inaccurate: our “calorie” is actually a kilocalorie, since a real calorie of energy is infinitesimally small.

        • You can actually test the Fitbit easily, at least on iOS. When you open the app, and it syncs, it then stays “connected,” and you can watch the steps increment. I’ve tested it in a number of situations, and steps are always accurate. There have been lots of other tests as well. In any case, any device you wear on your belt is much more accurate than a wrist-worn device.

  6. If walking for 20 minutes burned 212 calories we’d all be a lot thinner! Apple’s measurement seems a lot more realistic. Back when I tracked only distance by memorizing where I walked and then later using Map My Run, I would use 80 calories per mile to give me a sense of how many active calories I burned. Now that I have an Apple Watch, it seems quite realistic. For example, it shows 210 active calories for a 2.86 mile walk yesterday during which time my average heart rate was 111. Maybe that website you’re using has a problem and not Apple Watch. I think you need to jump much deeper into the science, which I suspect Apple has given the reliable-looking data I’m getting.

    • The Fitbi app lets you record walks and runs. I’ve only done it a few times, but for a 22 minute walk at roughly the same pace, it records 110 cal. Extrapolate that to a half hour, and it’s about 150 cal. That is still very far from what Apple is suggesting. I know there were several ways of calculating calories, and none of them are exact, but everyone I checked shows much higher numbers than Apple.

      • Your comparison is ridiculous…you’re just assuming that the FitBit is correct, and the Watch MUST be wrong because they 2 readings aren’t the same. The other possibility is that the FitBit is wrong, even if other trackers match it. Or yet a third possibility is what others have mentioned – calorie counting is a pseudo-science and nobody really knows what’s actually going on. Even the word “calorie” is inaccurate: our “calorie” is actually a kilocalorie, since a real calorie of energy is infinitesimally small.

        • You can actually test the Fitbit easily, at least on iOS. When you open the app, and it syncs, it then stays “connected,” and you can watch the steps increment. I’ve tested it in a number of situations, and steps are always accurate. There have been lots of other tests as well. In any case, any device you wear on your belt is much more accurate than a wrist-worn device.

  7. Look at your screenshot and you’ll see 144 total calories, which is nearly the same as the 150 from your Fitbit. We burn calories just to stay alive. Apple provides you with these resting calories as well as active calories burned from exercise. It also provides the total. Perhaps your Fitbit just provides the total. The website you used for your article states that it provides total calories and directs you elsewhere to calculate active calories. In other words, it looks like all this tracking is pretty much the same but you just need to know whether you’re getting active or total calories. Active calories is what you want, which is why Apple places it in large type. A commenter above said that the science is iffy. This isn’t true. About 10 years ago, scientists pretty much nailed calorie tracking, but there’s still a lot of confusion about active versus resting versus total calories. It also depends on your height, weight, and gender, which is why Apple asks you for this information. Using total calories can be dangerous. If you rely on total calories, you could gain weight rather than lose it. I’ll take Apple’s active calories to make sure that doesn’t happen!

  8. Look at your screenshot and you’ll see 144 total calories, which is nearly the same as the 150 from your Fitbit. We burn calories just to stay alive. Apple provides you with these resting calories as well as active calories burned from exercise. It also provides the total. Perhaps your Fitbit just provides the total. The website you used for your article states that it provides total calories and directs you elsewhere to calculate active calories. In other words, it looks like all this tracking is pretty much the same but you just need to know whether you’re getting active or total calories. Active calories is what you want, which is why Apple places it in large type. A commenter above said that the science is iffy. This isn’t true. About 10 years ago, scientists pretty much nailed calorie tracking, but there’s still a lot of confusion about active versus resting versus total calories. It also depends on your height, weight, and gender, which is why Apple asks you for this information. Using total calories can be dangerous. If you rely on total calories, you could gain weight rather than lose it. I’ll take Apple’s active calories to make sure that doesn’t happen!

  9. Your entire argument is based on the assumption that the online calculator you happened to use is accurate. Yet you failed to provide any information about the accuracy of the measurements. Calorie calculation is a science. If you want to discuss it, you’ll have to use data. All you’re doing is chucking stones at Apple corporation.

    • I compared several online calculators, and they all give numbers within a few percent of each other. Since Apple has fixed theirs, I think it’s pretty safe to assume they were wrong.

  10. Your entire argument is based on the assumption that the online calculator you happened to use is accurate. Yet you failed to provide any information about the accuracy of the measurements. Calorie calculation is a science. If you want to discuss it, you’ll have to use data. All you’re doing is chucking stones at Apple corporation.

    • I compared several online calculators, and they all give numbers within a few percent of each other. Since Apple has fixed theirs, I think it’s pretty safe to assume they were wrong.

  11. I’ve wondered about how it is calculated…every once in a while I forget to end my “other” work out and it continues to calculate my active calories as if I am still working out, which I am not…so if it isn’t using heart rate how is it calculating the calories?

  12. I’ve wondered about how it is calculated…every once in a while I forget to end my “other” work out and it continues to calculate my active calories as if I am still working out, which I am not…so if it isn’t using heart rate how is it calculating the calories?

  13. I have this problem too. For the last 4 months I’ve been using a HRM with bluetooth to phone and recording my workouts via digifit. Consisently for 4 months, every workout I do shows an average burn of 10 calories/minute.

    I got given an apple watch for my birthday…. tried it 4 times so far and my calorie burn is on average 5-6 calories per minute doing the exact same workout.

    So…. I did a workout yesterday, wearing my watch and my HRM. Both have the same stats as far as gender, age, weight and height. Both record my heart rate as the same. But the calorie burn results are very different. 305 (HRM) v 165 (Apple Watch) calories.

    I have been tracking my weight loss for the last 6 months and according to calories burned v carlories taken in my HRM and calorie burn is correct according to the weight I have lost.

    Apple is way off and needs to re-visit their formula for calculating calorie burned based on HR.

  14. I have this problem too. For the last 4 months I’ve been using a HRM with bluetooth to phone and recording my workouts via digifit. Consisently for 4 months, every workout I do shows an average burn of 10 calories/minute.

    I got given an apple watch for my birthday…. tried it 4 times so far and my calorie burn is on average 5-6 calories per minute doing the exact same workout.

    So…. I did a workout yesterday, wearing my watch and my HRM. Both have the same stats as far as gender, age, weight and height. Both record my heart rate as the same. But the calorie burn results are very different. 305 (HRM) v 165 (Apple Watch) calories.

    I have been tracking my weight loss for the last 6 months and according to calories burned v carlories taken in my HRM and calorie burn is correct according to the weight I have lost.

    Apple is way off and needs to re-visit their formula for calculating calorie burned based on HR.

  15. After the update my Garmin heartratemonitor is within a couple of calories of apples TOTAL calories. Also the average heart rate is the same as the gamin. Today’s workout had apple giving me a total calories burned of 298 and the Garmin at 306. Garmin said average heart rate for workout was 140, apple said 139. I’ve used this on walks, stair stepper, and elliptical. Hope this helps.

  16. After the update my Garmin heartratemonitor is within a couple of calories of apples TOTAL calories. Also the average heart rate is the same as the gamin. Today’s workout had apple giving me a total calories burned of 298 and the Garmin at 306. Garmin said average heart rate for workout was 140, apple said 139. I’ve used this on walks, stair stepper, and elliptical. Hope this helps.

  17. Seems like a lot of Appleites who want it to be right more than anything.

    I have Apple 4 and used it for HIIT on an elliptical many times. It says I’m burning about 520 calories (total) in 54 minutes.

    I compared avg HR and duration to two different Polar cheat straps and the AW was pretty accurate.

    I then entered the info into five different online calculators (age, weight, sex, duration, avg HR). All five were fairly consistent at 660 total calories.

    Huge difference.

    Calorie burn is critical to diet configuration if you’re trying to lose / maintain / or gain weight.

    Disappointed.

  18. Seems like a lot of Appleites who want it to be right more than anything.

    I have Apple 4 and used it for HIIT on an elliptical many times. It says I’m burning about 520 calories (total) in 54 minutes.

    I compared avg HR and duration to two different Polar cheat straps and the AW was pretty accurate.

    I then entered the info into five different online calculators (age, weight, sex, duration, avg HR). All five were fairly consistent at 660 total calories.

    Huge difference.

    Calorie burn is critical to diet configuration if you’re trying to lose / maintain / or gain weight.

    Disappointed.

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