Standard rebar hook and minimum bend diameter

The term standard refers to one of the following:

       - 180 degrees bend plus 4db extension but not less than 65mm at free end,
       - 90 degrees bend plus 12db extension, at free end of bar
       - For stirrups and tie 
                  a. 16mm diameter bar and smaller, 90 degrees bend plus 6 bar diameter 
                      at free end of bar
                  b. 20mm and 25mm diameter bar, 90 degrees bend plus 12 bar diameter 
                      extension at free end of bar
                  c. 25mm diameter and smaller, 135 bend plus 6 bar diameter 
                      extension at free end of bar.


Minimum Bend Diameter

The diameter of bend measured on the inside of the bar, other than for stirrups and ties in sizes 10mm diameter   through 15mm shall not be less than the following:
                    a. 6 bar diameter for 10 to 25mm diameter bar
                    b. 8 bar diameter for 28 to 32mm diameter bar
                    c. 10 bar diameter for 36mm diameter bar
The inside diameter of bend of stirrups and ties shall not be less than  4 bar diameter for 16 mm diameter bar or smaller. For bars larger than 16mm diameter, the diameter of bend shall be in accordance with the previous pharagraph
                  example: 
                              6 bar diameter, to arrive the length of bending just multiply the the bar diameter with 6
                               (i.e. 6x10=60mm)