Take a piece of paper out of your printer. That's the size of an A4. A4 measures: 21.0 × 29.7 cm (Make this 30cm)

Put the paper on your fabric and draw a line along the contour. Make sure to have at least 1cm seam allowances.

You are gonna fold the longest side in three parts later. The zipper is going to be sewed on the smaller sides.

Now make a triangle. His sides must measure as much as the longest side of the peace of paper.

So if you use A4, you can make a triangle measuring 10 + 10 + 10 as i did.

I used my compasses.

Don't mind the red lines btw ^^

Put it on your fabric and draw a line along the contour.

You will need 2 triangles. (Not 4, like on the picture). Make sure to have at least 1cm seam allowances.

Pin your open zipper on one side of the fabric so that it matches the drawn line.

Sew: fabric right side up & zipper right side down. Think inside out.

Sew the zipper on one side.

Sew the other side too.

Turn pouch inside out.

Sew one triangle on the pouch.
Make sure you sew the 'closed side' of the zipper first.

Than sew the other side. Leave your zipper open, so that you will be able to turn in outside-in again ;)

Finished!