Use their program at their website. Put in the load and the zero such as a 100 yards and it will give you the distance for each hasmark. Print a little sheet out and tape to the inside of scope lens cap or on the side of the rifles butt (laminate it first)
http://apps.vortexoptics.com/lrbc/

Example below is .243 95gr SST Hornady Superformace, scope is the Vortex viper 3-9X40..... The app link below figures out the hash marks for you and it is pretty accurate. Worked on my friends .223 when we were shooting it at 200 yards.

100 yard zero:
First hash mark 225 yards
Second 361 yards
Third 468 yards
Fourth 572 yards