It's not a good idea to think in inches with a scope, if you are using Iron Sights, have at it... you have no other choice, but scopes... bad choice.
To figure out MOA from Inches you use the following
Inches X 100 / 1.047 x Distance = MOA
To Convert MOA to Mils you divide the MOA by 3.43 to get the mil equivalent
The problem with Inches and what not, you have to then rely on distance where if you use TMOA or Mils you can ignore the distance and use the observed value. (providing your scope's reticle matches it turrets). Then 1 Mil observed from center is 1 Mil on the turret at any distance. Same with Matching MOA or IPHY scopes, 1 MOA observed is 1 MOA regardless of the distance. There is no multiplication.
Going to a ballistic Program like JBM Online which is FREE, you can tell the software to output your data in 2 units of your choice. You can mix and match to your hearts' desire.
Finally, if you have a Mil reticle and MOA turrets, it's best to use 1 MOA adjustment per .25 Mils observed in the reticle. (using the reticle like a ruler) So for every 1 Mil Dot you see you a have 4 MOA of adjustment. You can divide the distance between the dots into quarters, so .25 = 1MOA, .5 Mils = 2 MOA, .75 Mils = 3 MOA, etc.
All of this should be done before you leave the house, it's 2013, no form of any math should be done on the line. We can print data sheets, ranging charts, etc all before we leave. Then you just use the charts to determine your adjustment. No thinking, just reading... it's easier, simpler, etc. JBM is an awesome resource that can not only get you on target but teach you how to use these units to you advantage. Just because Iron Sight guys did "X" in 1978, doesn't mean we have to do it now. And trust me there formulas for wind and what not are absolutely incorrect for a 338LM, they were written for a 308 shooting a 168 and happen to work in a passable manner for a 5.56 out to 600 yards, but for anything else they are wrong. And people wonder why the wind is so wicked, they are using bad data that was barely valid 40 years because nobody bothers to run the formula for the correct constants. (yes there are other formulas)
Good luck... think Minutes or Mils, not inches... Unless you are using a scope that adjusts in IPHY then you can use inches.