Make a Pentagon from a Square or A5
Some origami models start with a pentagon instead of a square. In these situations you must make the pentagon before you can begin your origami project. Making pentagons from a square or a rectangular sheet of paper is not easy. The process takes many steps which leads to error and the resulting pentagon has numerous crease lines.
Below is a list of methods to make a pentagon from a square or a A5 paper. The instructions are organized so the perfect pentagons are listed on top, the near perfect pentagons are in the middle, and the least accurate pentagons are at the bottom.
Not Perfect, Easy to Make Pentagons
Some of the above methods make "theoretical" perfect pentagon but in practice, errors occur due to the thickness of the paper or the accumulation of small mis-alignments (human errors). The more folds there are, the more chances of errors.
Almost all pentagons will have crease marks running through the shape. Some creases are related to the geometry of a pentagon so they could be useful. Some creases have no relationship to the final pentagon so they are undesirable.
In most cases, the easiest pentagons are the least accurate; however, depending on your origami model, the pentagon might be "good enough".