I found myself in need of a 5x7 envelope the other day, so I sketched one on the back of a spare sheet of scrapbook paper and snapped a few photos, just in case you'd like to make one too!
All you need is a sheet of scrapbook paper, a ruler, scissors, and tape!
Sketch a 5x7 rectangle in the middle of the scrapbook paper (on the white side).
On each side, draw a triangle 4" in height.
Cut out the shape, and fold up three of the sides. Tape together.
Add your card, and send!