Here is a rough calculator to determine your final gear ratio.
You may have to enable active-X controls for this to work.

Drive Sprocket - Front  (# teeth) ----
Jack Shaft 1 -  (# teeth)---------------

Jack Shaft 2 - (# teeth)---------------
Driven sprocket - Rear (# teeth)-----

Final Gear Ratio :1

Use This Only as a Guide - You Should Always Check Your Own Math and Calculations