Use an 8.5″ x 11″ letterhead page (or the size required by your document)
Confirm the recipient’s address block and mailing window location (if using a window envelope)
Place the letter face down on a flat surface
Fold the bottom third up to the halfway point (so the bottom edge aligns with the top of the address block area)
Fold the top third down to cover the previous fold (so the top edge aligns with the bottom of the middle fold)
Crease each fold firmly with a ruler or fingernail
If using a window envelope, align the address so the folded letter’s address lines appear in the window area
Insert the folded letter into the envelope with the folded side facing down
Seal the envelope