Blkram, a minute of angle (moa) is a unit of angular measurement, 1/60 of 1 degree. Calculating the physical equivalent group size equal to one minute of angle can be done using the equation: equivalent group size = tan(MOA ∕ 60)*distance. In the example previously given and substituting 3600 inches for 100 yards, tan(1 MOA ∕ 60)∙ 3600 inches = 1.0471975511966 inches.
As a linear equation, 1 moa (or 1" for simplicity)at 100 yds would be 3.15" at 300 yds, and approx. 4.2" at 400 yds, etc.