I did not program it with my stride length. From what I am understanding about the unit, the number of steps are calculated based on your height and activity. I have been using the Ultra and have received my Fitbit ONE, but I haven't had time to work with it yet.
from p.16 of the user's guide: "Fitbit One calculates your distance based on your step count and stride length. Your stride length is estimated based on your height and gender. You also have the option of entering your own stride length for increased accuracy. Distance units can be set to either miles or kilometers by changing your settings."
Go to a walking trail with measured miles. Count your paces for a mile. Divide your number of paces into 63,360 (inches in a mile) that will give you your exact number of inches in your step. Going for the mile will give you an average which will be accurate.
In the time that I have been using the FitBit (I have used an ultra and recently upgraded) I have not seen any configuration for stride length. I assume that uses an averaged stride based on your height.
When you enter your gender and height in your profile, it sets an estimated stride length. Unfortunately, you can't see what the default is because the stride length fields are empty. The calculation for the default stride is based on this:
If you find your preset stride length isn't accurate for you (check by comparing the Fitbit distance with markings on a track, football field, or by walking some other known distance), you can calculate what it should be and change your stride settings for both walking and running.