What are the dimensions (size) of the pieces 3D origami
This video shows the size of the 3D origami pieces can be used. Among these sizes there are 1/2, ¼, 1/8, 1/16, 1/32, 1/64, 1/128, 1/256.
Take a sheet of A4, fold in half and cut
This will be the size for pieces ½ (one half)
Divide in half again and cut. this will size ¼
divide in half and cut. this will size 1/8
Divide in half again and cut. this will size 1/32
How to make these pieces sizes refer to the link above
How to make triangular pieces for 3D origami see here.
Also you can see others 3D origami tutorials.