How to calculate cutting length of Rings of rectangular column?

Example: Consider Rectangular Column 450mm x 300mm having cover to reinforcement 40mm.


 Size of the stirrup on 450mm side= 450-40-40 = 370mm
 Size of the stirrup on 300mm side= 300-40-40 =220mm          

Total cutting length of ring for 8 dia bar = Periphery + hook length.                         
                                                                  =2*370+2*220+2*8*10=1340mm

hook length= 10D