Sight Correction Calculator by SDM 

Plug in your own numbers and click for answer. 
This is a simple calculator based on the formula " error ∕ distance x sight radius = correction needed "
The important thing to remember is all units must be the same and expressed in decimal form ( no fractions )
In the example the page loaded with it shows our error to be 1.5" at the target, this could be in any direction , but will determine what direction you move the sight.
The distance to target is 720 inches ( 20 yards ) and the sight radius is 6.25" ( typical milspec 1911 with fixed sights )
With these parameters it shows a needed correction of .013"
So if it was shooting 1.5" high at 20 yards we would either have to lower the rear sight or raise the front sight by .013"
I hope you found this helpful.