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How to fold a letter for an envelope
For a plain, non-window envelope, use a standard tri-fold: fold the bottom third up, then fold the top third down over it. For a window envelope, use a Z-fold instead, folding so the address ends up facing outward and lined up with the window when the letter is inserted top-edge first. The two folds solve different problems and are not interchangeable.
Checked July 30, 2026/6 min read
Written by Claire PostReviewed against USPS Publication 28
What is on this page6 sections
Folding a letter seems too simple to get wrong, until it needs to line up with a window. A plain envelope forgives almost any fold, as long as the paper fits. A window envelope does not, since the whole point of the window is that the address on the letter itself becomes the envelope address, and a fold that is off by even half an inch can hide it behind the envelope material instead of showing it through the window.
Two different folds solve these two different problems, and most guides only cover one of them.
Step by step
Use a standard tri-fold for a plain, non-window envelope
Fold the bottom third of the page up, then fold the top third down over it, so the page ends up in three roughly equal panels. This is the everyday fold for a personal letter or a plain business envelope with no window.
Use a Z-fold for a window envelope instead
Fold the bottom third up the same way, but then fold the top third down behind rather than over, so the page forms a Z shape when viewed from the side rather than a simple flat stack.
Position the address so it faces the window when inserted
The address block needs to end up facing outward, roughly 2 inches from the top and a half to 1 inch from the left of the folded page, so it lines up with the die-cut window once the letter is inside.
Insert the letter top-edge first
The final fold, which was originally the top of the page, goes into the envelope first. This keeps the address facing the window and helps the letter slide in without catching or bunching.
Adjust for a double-window envelope by checking both windows before sealing
A double-window envelope shows the delivery address through one window and the return address through another, both pulled from the same folded letter. Before sealing, hold the folded letter up to the envelope and confirm both windows show the correct information, since a fold that works for one window can still misalign the other.
Quick reference
| Envelope type | Fold to use | Insert direction |
|---|---|---|
| Plain, no window | Standard tri-fold | Either direction, no alignment needed |
| Single window | Z-fold | Top edge first, address facing the window |
| Double window | Z-fold, checked against both windows | Top edge first, verify both windows before sealing |
Special cases
The rule above covers most people. Here is what changes for the rest.
What if my letter is longer than one page?
Fold all pages together as a single stack, treating them as one unit for the tri-fold or Z-fold. Do not fold each page separately, since that creates a bulkier, less even result and can throw off window alignment on a window envelope specifically.
My letter does not line up with the window even though I used a Z-fold. What is wrong?
The most common cause is the address block sitting in the wrong position on the original page before folding, rather than a folding mistake itself. Check that the address is positioned roughly 2 inches from the top and a half to 1 inch from the left of the page, since a Z-fold can only show the window whatever is already in that position, it cannot correct a misplaced address block.
Does the fold matter for a card, like a greeting card, or just a printed letter?
Cards are generally not folded at all, since they are usually already the right size and thickness for their envelope. Folding applies specifically to a full sheet of paper, a printed letter, being reduced down to fit a smaller envelope.
Key terms on this page
- Tri-fold
- The standard letter fold for a non-window envelope: bottom third up, then top third down over it, creating three flat panels.
- Z-fold
- The fold used for a window envelope, positioning the address to face outward through the die-cut window once the letter is inserted.
- Double-window envelope
- An envelope with two windows, one showing the delivery address and one showing the return address, both pulled from the same folded letter.