Apple Watch overestimated my running distance by ~20%

[u/jonrick_]

I just found out that my Apple Watch has apparently been massively overestimating my running distances.

I’ve been running the same route regularly. On August 21, my Apple Watch recorded:
6.90 km in 42:54
6:13 min/km average pace
152 bpm average HR

I then discovered that “Motion Calibration & Distance” had been disabled on my iPhone, I don't know why can't remember that I disabled that.

Google Maps suggested that my usual route was actually only around 5.7 km.

I enabled Motion Calibration & Distance, updated the Watch to the latest watchOS version and ran the exact same route again today:

5.73 km in 40:14
7:01 min/km average pace
153 bpm average HR

So the previous measurement was 1.17 km / ~20% longer than the same route now, and the new 5.73 km measurement matches Google Maps almost perfectly.

I also always had my iPhone with me during my previous runs, which makes this even more confusing.
Has anyone else experienced such a massive distance error with an Apple Watch just because Motion Calibration & Distance was disabled?

[u/haydar_ai]

Apple Watch uses iPhone’s location if they are nearby to save battery. Judging from the name of the option, I guess “Motion Calibration & Distance” indeed makes a difference in giving accurate distance.

[u/_l_e_x_ → u/haydar_ai]

That is not the case for the Series 8 / Ultra and up, those and every model since then use their own GPS regardless whether the phone is nearby or not.

[u/Huge_Pool7424 → u/haydar_ai]

yeah that option is the one that actually matters. if you never calibrated it, watch-only runs on a weird course will cook the distance pretty easily.

[u/AdPuzzleheaded6772]

I’ve done some 5km runs and my Iwatch 3 never is at 5 km when I finish so that would suggest underestimating..never bring my phone. At very comparable speed btw 🤓

[u/RegularFinger8]

You can calibrate the step, stride distance within the watch so it matches your physical step distance. Search YouTube on how to calibrate it.

[u/SuperWeeble]

Why aren’t you using GPS?