I do this by just rounding 1.047" to 1". So... 1 Minute Of Angle (MOA) is about 1" at 100 yards, 2" at 200 yards, 3" at 300 Yards, etc. I can do the math in my head this way.
Then at 100 yards a target measuring 1 MOA in the scope is a 1" target. ( 1 X 1 = 1)
At 200 yards a 1 MOA target is 2" (2 X 1 = 2")
At 300 yards a 1 MOA target is 3" (3 X 1 = 3")
At 600 yards a 2 MOA target is 12" (6 X 2 = 12")
At 650 yards a 2 MOA target would be 13" (6.5 X 2 = 13")
I do a lot of long range practice by shooting at rock faces and measure my group sizes with this method.