I was recently looking to do some data analysis of my historical exercise data stored by Garmin, so I requested a data export through their web site. When the export was ready and I downloaded and started playing with it, I discovered something very weird: the “calories” value for each activity in the “summarizedActivities.json” was several times higher—about 4.18 times higher, to be precise—than the calories displayed for the same activity in the Garmin Connect app. (If just seeing “4.18” is enough for you to see where this is going, then you’re one step ahead of where I was!)
I filed a support ticket with Garmin asking how to interpret the field given that the values in it don’t make any sense. They sent back a useless response.
While debating how to best explain to them that their response was useless, I had a brainstorm: “Hmm, I think Garmin is a European company. I wonder if Calories are actually measured differently there or something?” So I took out my phone and started to type out the search, “are calories measured differently in Europe?”
I had gotten exactly two words into typing out that search, i.e., “are calories”, when this appeared in the at the top of the search results: “1 calorie = 4.18400 joules”.
Aha! Apparently, even though the fields in the data export are labeled “calories” and “bmrCalories”, they’re actually joules, not calories, and you can convert them into calories by dividing them by 4.184.
My Google-fu was not strong enough to find any evidence that anyone else on the internet has grappled with this particular question and figured out this answer, so I’m posting this for the benefit of future exercisers / data nerds. If you stumbled upon this page because you were searching for an answer to this question, drop a comment below to let me know!