I love crafty afternoons.
You can use this method to make any size bag you like, the only rule to follow is that the base and the sides are folded to the same measurement. The dimensions in the below instructions gave me bags that were approximately 12 x 24 cm. Also, don't be scared with the number of steps or photos below! I get confused when talking about folding this edge, easing that crease, taking this side...etc etc, so I compensated by taking waaaay too many pictures!
How to make a gift bag
What you need:
1. Cut out your paper 28 x 35 cm.
2. Turn the paper so that the long side is facing you, fold in half.
3. Fold the two edges over and 4. glue down.
5.6.&7. Measure 2.5cm in from the glued edge and fold the paper over. Repeat on the opposite side.
8.9.&10. Next open one of these sides out. You will have three crease lines, one of the outer creases will be inverted, reverse the crease.
11.&12. Invert the middle line so that the two outer creases meet. Repeat for the other side.
13. Turn the paper round so that the short ends are facing you. Fold the ends over to create a thin seam, glue the seam down.
14. Measure 2.5cm in from the edge and fold the paper over. Open out and fold along the same crease the opposite way - this will make open the bag out a tad easier.
15. 16. 17.&18. Unfold and put your hand inside the bag to open out the bottom. Gently push the sides of the bag out to create the block bottom. This is the fiddliest part but you can use the ruler to open it out to create sharper lines.
You've now finished the bag and it's ready to be prettied up! But if you're making a supply for future use then you can fold the sides in and the bottom of the bag up so that they can be easily stored without damaging them. (19 &20)
Warning to any friends and family - expect your future presents to come in brown paper bags from now on!