There's more to folding a letter than you might think, especially when it comes to business etiquette. Familiarize yourself with the correct ways to fold and insert a letter into an envelope.
Steps to Follow
How to Fold a Standard US Business Letter for a Business Envelope

Addressing the Envelope: Before inserting your letter, handwrite or print the recipient's address in the center of the envelope. Place your return address in the top left corner.

Position the letter face-up on a flat surface. Confirm that the address on the letter matches the one on the envelope and ensure you've signed the letter. The text should be oriented towards you, as if you're reading it.

Begin by folding the bottom section upwards. Grab the bottom edge of the paper and fold it upwards, aligning the bottom edge to about one-third of the page's height. If uncertain, place the envelope beneath the letter to serve as a guide.

Align the edges carefully. Prior to finalizing the fold, ensure the sides of the letter are perfectly aligned to prevent uneven folds. Once aligned, use your finger to create a sharp crease.

Next, fold the top section downwards. Fold the upper part of the letter so that there's approximately half an inch (about 1 cm) of space between the bottom and the newly folded top edge. Use the envelope as a guide for accuracy.

Finalize the fold at the top. Ensure the top fold aligns with the paper's edges to achieve a clean, straight fold. For a neat crease, you can use a ruler's edge to press firmly along the fold.

Slide the letter into the envelope. Orient the letter so the folded sections face outward, aligning the top fold with the envelope's opening. Hold the envelope with its flap facing you and ensure the letter slides in smoothly without wrinkling.
Preparing a Standard US Business Letter for a No. 10 Windowed Envelope

Ensure proper letter formatting. When using an envelope with a clear window for the recipient's address, align the letter correctly to display this information through the window.
- Set your margins to 1 inch (2.5 cm) on all sides in your word processor and left-align the text for the date and recipient's address.
- The letter should be single-spaced with a double space between paragraphs, maintaining a left alignment.
- Leave approximately 2 inches (5.1 cm) of space from the top of the page to the date.
- Write the date in full (e.g., April 1, 2016).
- Press enter twice to create a blank space between the date and the recipient’s details.
- Type the recipient's full name, press enter, and add the recipient’s address, followed by the city, state, and zip code. Ensure a space between the contact details and the salutation.

Adopt the “z-fold” technique for the letter. To showcase the recipient's name and address through the envelope's window, fold the letter accordingly.
- This method sacrifices some privacy compared to inward folding, but it's essential for the windowed envelope to display the name and address.
- For confidential content, it's advisable to use a standard envelope without a window.

Position the letter with its text facing downwards. This orientation will help you locate the recipient's name and address for the fold.
- If executed correctly, the letter's content should be unreadable.

Position the letter upside down. Place the letter with the text facing down, ensuring the recipient’s name and address are closest to you.
- If done correctly, when you glance beneath the paper, the recipient's name and address will be nearest to you.

Fold the upper part downward. Fold the top third of the paper towards you.
- If unsure about the measurement, align the envelope beneath the paper's center as a guide.

Bring up the bottom part. Fold the bottom third of the paper upwards and away from you.
- Now, the recipient's name and address should be visible to you.

Place the folded letter into the envelope. Ensure the recipient’s details face the front of the envelope and show through the window.
- If the recipient’s details aren’t visible, the letter might be inserted upside down. Rotate the letter (ensuring the recipient’s details still face the window).
Preparing a Standard US Business Letter for a Small Business Envelope

Verify the address. Prior to folding, ensure the address inside the letter matches the one on the envelope.
- This step helps prevent any confusion.
- Ensure you've also signed the letter.

Place the letter on a flat surface. Confirm the text faces upward and is visible to you. This is your final opportunity to proofread and check for any omissions.
- For instance, have you included the date? Are there any spelling or grammatical errors?

Fold the lower portion upwards. Fold the bottom of the letter so it aligns approximately half an inch (about 1 cm) from the top.
- Using the envelope as a guide, ensure the folded letter is compact enough to fit inside.

Ensure a straight crease. Align all outer edges of the paper before making the fold to avoid uneven creases. A misaligned fold could cause the letter not to fit the envelope.
- For a crisp crease, use a ruler. Hold it sideways and slide its thin edge along the creases to flatten them.

Fold the letter's right side inward. Take the right segment of the letter and fold it approximately one third of the way in.
- Align the letter's top and bottom edges, then crease the fold.

Fold the letter's left side inward. Take the opposite side of the letter and fold it a third of the way in, mirroring what you did with the right side.
- Ensure the top and bottom edges align perfectly before making the crease.

Position the letter horizontally and place it in the envelope. Insert the letter with the latest crease going into the envelope's bottom first, ensuring the folds face the envelope's rear side.
- This orientation assists the recipient in easily locating the starting point to unfold the letter.
Recommendations
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Always review your letter before placing it in the envelope to avoid any embarrassing errors.
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For neat folds, utilize a ruler to flatten them completely.
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Remember to affix a stamp to your letter prior to mailing it.
Cautionary Notes
- If you're sending multiple pages, it's advisable to take your letter to the post office. Postage costs may increase if the weight exceeds the standard limit.