How accurate is it?

[thybountyhunter]

At this time I started to do runs at my local gym which on the treadmill you are allowed 30 min and then it applies a 5 min cool down.

Yesterday I did a 5.12km run in that time, however when I look at my fitbit and I had set the exercise to treadmill it is showing I did 6.12 kilometers.  I know my steps are 0.9 meters so the movement of my arms will help dictate the calculation to distance travelled but a treadmill will calculate how much distance was travelled based on how fast it goes etc...

Who is more accurate or what one should I rely on?

[JohnnyRow]

I'm not sure you'll be able to get  a definite answer to that.  I believe treadmill calibration can be off a bit, and they can have some slippage too, maybe somewhat depending on maintenance.  But also any error in stride length gets multiplied with every step. It sounds like you have looked at where Fitbit sets stride length.  Maybe you have noted there are separate settings for walking and running stride lengths too. I think "Treadmill" setting always used walking stride length.  You might try using the fitbit exercise mode of "running" next time  to get the running stride length, except if you have a tracker with built-in GPA, you would want that turned off.  OR you could stay with treadmill setting and set your walking stride length to what you running stride length is at, remembering you running length is, to reset to afterward.

Plus your stride length probably changes during the cool-down as you slow down.   Maybe you want to check mileage on treadmill and fitbit at start of cooldown to see how they compare then.

So not a simple answer but if I had to choose one or other, I would say treadmill is probably closer.  You could just adjust stride length to match treadmill if want an easy solution.

[YachatsMike · Accepted solution]

The Fitbit derives a distance based on an algorithm.  The treadmill actually measures the amount of belt that went under your feet.  I'd believe the treadmill.

If you were actually walking on the street and the Ftbit was using GPS, I'd go with the Fitbit.