As always, safety is first and foremost when handling your firearm.
Using dial or digital calipers set to inches, measure your current front sight from the top of the slide to the top of the front sight.
The sight radius is the distance between the BACK of the Rear Sight to the BACK of the Front Sight.
The impact radius is the distance between your bullet's impact and your point of aim.
The target distance is the distance between your gun and the target. 20 yards (720") is an ideal distance.
Choose the Dawson Precision Perfect Impact® sight height closest to this impact corrected front sight height.
As long as it is within .005", this should be more than adequate for precision pistol shooting. Custom sights are available at an additional charge.