2 people big age gap, both with fitbit3, run same length together, 1 fitbit gives different results

[Johnz555]

Myself and son, 61 and 27, both with fitbit 3, run together each day. Alongside each other so exactly same length of distance. My fitbit says 3.89 km and his says 4.9 km. How is this if we;ve run alongside each other for the whole distance,start/stop together, slow down speed up together yet around 1km difference when we both press FINISH....Dont tell me Age has something to do with the stats?

We are both same height also, 5'9. 

[JohnnyRow]

You didn't specify whether or not you are connected to phone's GPS.

[Johnz555]

hi, my one isnt, not sure if son;s is, but why does that make a diff if its coming up with a distance figure for both of us, so its tracking our running, i..e the fitbit hasnt stopped working just because my phone is not on me and sync'd?

[JohnnyRow]

There are 2 totally different ways of getting distance.  If using connected-GPS, it uses phone's GPS to get distance.

If not connected to GPS, it calculates distance as number of steps times stride length.  If stride length is set wrong, distance will be wrong.

See How does my Fitbit device calculate distance traveled? 

and Can I change my stride length in my Fitbit account? 

[Johnz555]

Ah, gotya Johnny, well thanks for that mate. I'll take the phone tomorrow and see how it fairs..Cheers again...and for the links