Folding envelopes and letters is often a skill required for sending correspondence and documents through the mail. As a general rule, whenever you are mailing legal documents, you should not fold them, but enclose them in a large enough envelope that allows the document to remain flat. There are many situations calling for the folding of letters or envelopes. Many mail-in offers require the sender to enclose a self-addressed, stamped envelope in the envelope containing the order form or offer. Folding letters, whether for personal or business purposes, is a practical skill.
Place your letter on a flat, hard surface such as a desk or table.
Use a ruler to measure the length of your letter's paper and divide this measurement by three. According to English Plus, business letters and other letters should be divided into thirds, horizontally, folded two times, before being put into the envelope.
Grasp the top edge of the paper, and pulling the paper down toward the side of the letter facing you, make a horizontal fold along the first section (the top 1/3 of the paper). Use your fingernail to press down on the fold, making a crisp crease.
If your envelope has an open rectangle or a window requiring the mailing address on your letter to be visible, fold this section of your letter back instead of forward. The top one third of the letter facing you will be folded backward, and according to English Plus, the letter will resemble a letter Z when the folding is complete.
Measure up from the bottom edge of the paper, forming the bottom 1/3 of the paper, and make another horizontal fold. Grasp the bottom edge of the paper and fold the bottom section of the letter over on top of the previously folded top section of the letter. Your letter now has two folds and three even sections. Use your finger to crease the fold.
Insert the letter into the envelope. According to English Plus, some personal stationary is shaped differently, so you might have to fold the letter so it fits the envelope size. For example, for very square envelopes, fold the letter in half vertically, and then fold the letter in half again horizontally.
Place the standard business size envelope measuring 4 1/8-inches wide by 9 ½-inches long, horizontally, onto a flat surface, such as a table or desk.
Grasp the left edge of the envelope and fold it toward the right about 3 ¼-inches. Crease the fold with your fingernail by pressing downward and sliding along the fold.
Grasp the right edge of the envelope and fold it toward the left about 3 ¼-inches. Crease the fold so the envelope lies as flat as possible, thus reducing bulk within the mailing envelope.
Insert the envelope into the mailing envelope. For personal stationary size envelopes that may be square, fold the envelope in half vertically.