If you have trig functions on your calculator
tan^-1(group size ÷ range) x 60 = MOA
Your calculator may mark the arctan function “arc” or even arctan.
It is imperative that the units used for group size and range be the same, so if the group is 1.5 inches in diameter, the range must be 3600 inches, not 100 yards. For that 1.5 inch group the calculation is:
tan^-1 (1.5÷3600) x60=1.4 MOA (yah, yah, 1.4324 etc. but sig figs!)
Gee, I'd love to see your data!