I'm not going to discuss or talk about the whys here. You can find a good post on that on fanhome. This is just to put into "stone" the formula for people to reference.

     plus
     = 1.0 * 1b 
     + 1.6 * 2b 
     + 2.2 * 3b 
     + 3.0 * HR 
     + 0.7 * nibb 
     + 0.7 * hbp 
     + 0.4 * ibb 
     + 0.4 * sb 
     - 0.4 * cs 

     minus
     = AB-H + SF + CS 

     LWR = plus/minus 


To convert to runs, you can use these estimators: 
     RC/out = .47 * LWR  - .10 
     RC     = .47 * plus - .10 * minus

     LWTS   = (.47 * LWR - .27) * minus
            = .47 * plus - .27  * minus