Gather materials: paper, ruler, pencil, scissors, glue or tape
Choose an envelope size
Cut a rectangle of paper for the envelope front
Fold the paper in half to create a crease, then unfold
Fold the left and right sides toward the center so they overlap slightly
Mark where the side flaps meet, then unfold
Fold the top edge down to form the top flap, then mark the fold line
Cut or trim the bottom edge if needed so it aligns with the side folds
Apply glue or tape to the marked areas for the side seams
Fold the sides in and press to seal
Apply glue or tape to the bottom flap area
Fold the bottom up to seal
Leave the top flap unglued so it can open and close
Crease all folds firmly and trim any excess paper