How to Fold a Letter for a Window Envelope (With Template)

To fold a letter for a window envelope, use a Z-fold. Crease the page at 3-7/8 in and 7-1/2 in from the top, a little taller than even thirds, fold the bottom section up, then fold the top section back so the address panel faces out. For a standard #10 double-window envelope, put the recipient's address in three lines starting 2-1/4 in from the top of the page and 1 in from the left, with your return address 1 in from the top.

Other boxes put the windows elsewhere; the table below covers them. Here's the standard layout. Your address shows through the upper window, the recipient's through the lower:

Top edge of an 8.5 x 11 in page
1 in     {{your_name}}
         {{your_street}}
         {{your_city_st_zip}}
2.25 in  {{recipient_name}}
         {{recipient_street}}
         {{recipient_city_st_zip}}
3.875 in --- fold: folds back ---
         Dear {{recipient_name}},
7.5 in   --- fold: folds up ---

Z-fold or C-fold: which way the address faces#

A Z-fold leaves the top section of the page, the part with both addresses, on the outside of the folded letter. That's the panel the windows need to see.

1. Set the letter face up, top edge away from you. A letter of several pages folds as one stack, page one on top.
2. Fold the bottom section up along the 7-1/2 in line and crease it.
3. Fold the top section back, away from you, along the 3-7/8 in line. Look at the edge: it's a Z.
4. Turn the letter over so the addresses face you, right side up.
5. Put the address panel against the windows and push it in crease first, so the top edge of the page ends up near the flap.

A C-fold, where both thirds fold over the front like a brochure, hides the address inside. If a C-fold is what your hands know, start with the page face down: fold the bottom section up, then the top section down over it, and the address ends up on the outside (wikiHow shows the window-envelope fold with photos (opens in new tab)).

Where the address goes on the page#

The windows decide where the address goes, and they move from box to box. Envelope sellers list each window by its size and its distance from the envelope's left and bottom edges. A #10 envelope is 4-1/8 by 9-1/2 in. Here are two common ones:

The address has to fit between two lines on the page. For the top line, add the window's height to its distance from the bottom of the envelope, take that from 4-1/8 in, and add 1/8 in. For the bottom line, take the window's distance from the bottom from 4-1/8 in, then subtract 1/8 in and another 1/4 in for the slide. For the standard double window that gives 2-1/4 in and 2-3/4 in: half an inch, or three lines of 10-point type.

Folded this way, the letter is 1/4 in shorter than a #10 and 1 in narrower, so it slides inside. Folded in even thirds it slides almost 1/2 in, and a three-line address can't keep USPS's clear space in a 1-in window; that's why the top panel is taller. Keep the address 1 in from the left edge of the page, as 4over4's window envelope guide (opens in new tab) does, keep it to three lines, and keep each line under 2-1/2 in, about 28 capital letters at 10 point. Keep your return address lines under 1-3/4 in. Leave the space below the address empty, too, so a date or reference line can't slide into view.

USPS sets the rules for what shows through the window in DMM 601.6.3 (opens in new tab):

• Every character of the delivery address must stay visible through the window, wherever the letter slides inside the envelope.
• At least 1/8 in of clear space must separate the address from each edge of the window, at every position.
• The address must be printed on white paper or paper of a very light color.

USPS also prefers addresses without punctuation (Publication 28, section 222 (opens in new tab)). For what goes on each line, see how to write each address line. Sending an invoice? Mailing an invoice in a window envelope covers remit-to addresses and reply envelopes.

If you're writing to two people at two addresses, each person needs a letter with their own address block.

Get the window envelope letter template#

Put your return address 1 in from the top and the recipient's at 2-1/4 in in three lines, both 1 in from the left. Keep the space under them clear until the letter starts, add nothing above the addresses, and fold at 3-7/8 in and 7-1/2 in. The positions come from supplier specs, not from your box, so print one sheet and tap-test it before you print the rest. If your box has a single window, move the recipient's address down to between 2-5/8 and 3-1/4 in from the top and put your return address on the envelope.

Building the layout yourself? Set the page margins in Word (opens in new tab) or Google Docs (opens in new tab) (Docs only shows margins for documents in pages format, not pageless). Then put the addresses in a table with the borders turned off rather than spacing them down with the Enter key, so a font change can't move them.

Test one before you print the rest#

Print one copy on plain paper, fold it, and slide it into one of your envelopes. Knock the envelope against the table on all four edges, checking both windows each time. The whole address should stay in view, with a little white space around it, every time. If it doesn't, move the block and test again.

The usual misses:

• Only the top lines show. The address is too low, often because the layout was made for a single-window box. Run the rule above for the box you have.
• The last line drops out of sight. The block is too tall for the window. Cut it to three lines, and check the fold; even thirds slide twice as far.
• Letterhead pushed it down. Measure from the top edge of the page, letterhead included.
• Blank paper in the window. It was folded backwards or went in the wrong way round.
• A long company name runs past the window. Shorten the line or split it in two.
• Tinted paper. USPS wants white or very light paper behind the window.
• The envelope bulges. A #10 holds about six folded sheets; thicker letters go flat in a 9 × 12 envelope.

If you're sending documents with the letter, fold them in behind it, and list them in an enclosure line.

Or skip the measuring and folding. If your letter is in Word or Google Docs, save it as a PDF, then upload it and we print, fold and mail it by USPS First-Class Mail to any US address. Postmarkr adds a separate address page in front of your letter, and that page is what shows through the windows of a #10 double-window envelope, so your layout never has to line up with anything. Up to six sheets, counting the address page, fold into the #10; longer letters travel flat in a larger envelope. A one-page letter in black and white is $2.05, which covers printing, the address page, the envelope and postage. Our print partner adds a small code strip in the bottom-left margin of every page, and black-and-white letters print in grayscale.

Questions about window envelope letters#

Which way does the address face in a window envelope?#

Out, toward the windows, and right side up, with the crease just below the address going in first. If the window shows blank paper or the body of your letter, it went in backwards.

Why does my address sit too low in the window?#

The layout was usually made for a different box. A single-window envelope's address starts at about 2-5/8 in, lower than a standard double window's 2-1/4 in, so a template built for one shows only half the address in the other. Letterhead or an extra blank line at the top does the same. Find the window sizes on your box or the seller's listing, run the rule above, and tap-test again.

What if my envelope's window is on the right?#

Some #10 envelopes put the window on the right, and seller listings don't agree on exactly where, so measure your own box. The height rule stays the same. For the left edge, measure from the envelope's left edge to the window and add 1/8 in; that's where the address starts on the page. The letter can slide a full inch sideways, so every line has to end 1-1/8 in before the window's right edge, measured the same way.

Will six or seven sheets fit in a #10 window envelope?#

A #10 holds about six folded sheets; Washington State's envelope template (opens in new tab) allows up to seven, including inserts. Plan around six. Past that, mail it flat; when a thick letter goes flat explains the size limits. With Postmarkr, up to six sheets including the address page fold into the #10, and a seventh sends it flat.