To use the 3R calculator:
Input (to nearest mm) the measurements requested in the left hand colomn. Then click on 'work it out' button

 
Measure (mm)
Calculated space required
   Proposed extractions
Crowding lower 3-3
   
Lower centre line shift (left or right)
   
If centre line shift exists: is it to Right or Left?
   
 
   
Crowding lower right 1 - 3
Lower Arch RHS
Crowding lower right 4 - 6
   
Space required lower right
Lower arch, LHS
 
   
Crowding lower left 1 - 3
Upper arch, RHS
Crowding lower left 4 - 6
   
Space required lower left
Upper arch, LHS
 
   
Move required to get upper right 3 Class I
   
Crowding upper right 4 - 6
   
Space required upper right
   
 
   
Move required to get upper left 3 Class I
   
Crowding upper left 4 - 6
   
Space required upper left