Always subtract the flight off the wall from the pool length to get a true stroke count for the distance you actually stroked - since what you are after is stroke length. Stroke length is how far you move forward on each stroke, also referred to as distance per stroke or DPS.
Stroke length = yards stroked / stroke count (spl). Example: 25 yard pool, swimmer takes 20 strokes after a 5 yard flight off the wall, so stroking 20 yards, then SL = 20 yards / 20 strokes = 1 yard or 3 ft.
Ideally we want you in the "green zone" where SL is between 50-70% of swimmers height (or wingspan). In the above example if swimmer was 5' 2" or 62", SL @ 36" (or 3 ft), green zone = SL/height = 36"/62" = .58 or 58% Do the math and see if you fall into the "green zone" 50%-70%