Which is more reliable - iPhone or treadmill?

Hi all, thanks for considering my question. I have a late model phone (iPhone 13) on which I use the Nike Run Club app. Lately I have been doing a number of training runs on a good quality treadmill. If say I set it for 12 minute miles, slightly uphill, and I run for an hour, the treadmill says I ran 5 miles, but the Nike app says I ran 6.1 miles (varies slightly). I know the late model iPhones have hardware/software to detect pace, movements, etc., and the Nike app has an "Indoor" setting specifically for treadmill running. So which is accurate? I have to say there was no calibration on the treadmill, so I guess it knows how far I ran by running 5 miles of tread material across the rollers? But is there a way I may be running - in air longer, longer stride, etc. - which makes the Nike app more accurate? I do see my pace varies on the app, by mile. I thought about trying to calibrate by running outside, but the terrain is so varied I don't know that it would be an accurate comparison to what I am running on the treadmill.

Does anyone have an idea on this? Thanks!


    It's generally considered that phones are unreliable when measuring distance and I would have thought that they'd be even less accurate indoors.   

    Most runners use a GPS watch and run outside.

  • TTTT ✭✭✭
    I tend to go with the TM. I cross check with the number of steps I have done, I know my stride length on the TM and then can work it out. 

    Running outside is good to do, I don't do much in winter because of the weather but there is more to look at! 

    I won't worry too much, if you are enjoying running and you are running for an hour then work on increasing the time or the pace over a period of time. Maybe start parkrun? 
  • Great, thanks for the insight all. It seemed to make sense the TM was more accurate just by how it works. Thank you! (and PS - I do run outside - coming out of winter I have done a lot of treadmill to keep up my training during spells of iffy weather!)
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