This is a jig I to help add peg holes to your Ikea KALLAX shelf. I assumbled my KALLAX without a few of the dividers, which allowed for larger shelf areas. Those dividers can then be used as shelves to split the regular 33cm x 33cm shelves in half, for smaller objects.

The jig is designed to hook onto the floor of one of the shelves and provide a spot to drill a hole where the new shelf peg will go.  Since the Kallax shelves are 33cm (330mm), the shelves are 16mm wide, and assuming a 5mm peg hole, the template provides a hole at (330 - 16 - 5) / 2 = 154.5mm above the lower shelf. The shelf should evenly divide the 330mm space into two 157mm spaces (accounting for the space lost to the shelf itself).

Hook the jig onto the lower shelf and press it against the wall. with a 5mm drill bit and an appropriate stopper (I just used tape to mark where to stop), drill an appropriate hole for your pegs.