A Long Walk to Calibrate Your Pedometer
This is essentially the same as the Short-Distance Walk except for two differences: (1) it's longer, and (2) you usually aren't going to know the distance involved ahead of time. Go for a walk—a long walk. The longer, the better. Walk for an hour or more, and memorize precisely the route you follow. Record your step count for the walk.
When done, you'll need to measure the distance you walked. I prefer to use a distance-measurement tool online to map out walks and calculate the distance traveled. You could also drive the distance and let the odometer on your car tell you the distance, assuming your walk doesn't take you where a car would not be allowed to travel. If you have a bike with an odometer, you could also ride the same route to measure its distance.
Now divide the distance you walked by the number of steps you took. That's your stride!
For example, I recently walked a large loop around Alki in Seattle counting 10,388 steps. I mapped the route on our distance-measurement tool, which popped out a distance of 5.9 miles. Our tool will even spit out the distance directly in inches (or centimeters, for those who prefer the metric system) so you don't have to convert from miles to inches yourself. On my walk, the tool says I covered 375,378 inches. The math from there is easy:
375,378 inches / 10,388 steps = 36.1 inches/step
Pros: Generates a very accurate measurement of your stride under normal walking conditions, which includes the time it takes your body to warm up, hopping curbs, crossing streets and other day-to-day distractions of walking in a normal environment.
Cons: It'll take some effort to walk a lengthy distance, and additional effort to determine the length of the route you walked.
Suggested Use: If most of your walks are relatively long jaunts through urban environments, this will likely generate your best stride measurements.
Distance Measuring Tool: Use this to calculate the distance along a given route. It's free to use and will automatically show your distance in inches (or centimeters) so you don't have to manually convert from miles or kilometers!