Distance reading on Apple Watch series 7 versus treadmill reading

I have recently bought an Apple series 7 watch and found that whilst running on my treadmill it is measuring in excess of my treadmill reading (6km coming out as 8km). This never occurred on my Fitbit where I had to input Stride length but my Apple only wanted my height and weight. I have tried calibrating by the outside walk etc but it is still not matching up to the treadmill reading. Is there a way to enter Stride length into my Apple to see if this fixes the issue?