Distance accuracy

[Bauerclan13]

I purchased a versa for my daughter who is into cross country and have been training with her. She runs and I speed walk but her Fitbit always ends with less miles that me even when she goes much further than me. I use an Apple Watch for myself. If she goes at least a mile farther than me y isn’t it showing her miles?

Moderator edit: subject for clarity

[JohnnyRow]

Is she using GPS, connected from phone, or just Fitbit alone?  That affects how distance is measure.  I don't know if Apple Watch has built-in GPS.

[Bauerclan13]

She does not bring her phone with her

Sent from my iPhone

[JohnnyRow]

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@Bauerclan13 wrote:
She does not bring her phone with her

Sent from my iPhone

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In that case, distance is calculated as number of steps times stride length.  Assuming Fitbit is getting the step count correct, or nearly so, her stride length might be off.  Fitbit assigns a default stride length based on physical data such as height, etc but that naturally varies by person.

See How does my Fitbit device calculate distance traveled? 

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

One way of adjusting stride length if you have a known distance course, a track would be great, is to run the known distance, see what distance Fitbit calls it. and adjust the stride length proportionally.  For instance if Fitbit measures the distance 10% too short, try increasing stride length by 10%, maybe having to give it a couple of rounds of adjusting to get it correct.  But be aware it cannot be exactly precise, as could only come with GPS, as stride length naturally varies somewhat with speed and terrain.