The #6¾ envelope: size, uses and what fits

What the #6¾ envelope is for

The #6¾ (3⅝ × 6½ in) is one of the smallest envelopes in the US commercial range, and it is sized for papers that are already small. Its classic job is the remittance, which simply means sending a payment: a personal check plus the payment slip torn off a bill, mailed back to the company that sent it. A standard personal check slides in flat and the slip lies on top of it, so neither has to be folded.

That is why billers and charities often enclose a #6¾, already printed with their own address, as a reply envelope when only a check and a slip need to come back. Outside of bills, it suits short personal correspondence, such as a thank-you note or a few lines written on a half sheet. It also holds a gift card that would slide around in a bigger envelope.

Which folds of US Letter paper fit

With a full sheet of US Letter, the usual folds don't work. The familiar fold in thirds leaves a packet that is still 8½ inches wide, two inches longer than this envelope, which is why that fold belongs in a #10. Folding the sheet in half twice brings the length down to 5½ inches, but the packet is then 4¼ inches tall, more than the envelope's short side.

What does fit takes two steps: fold the sheet in half from top to bottom, then in thirds from side to side. That gives a packet a little under 3 × 5½ inches, which slides in lengthwise with room to spare. A half sheet (5½ × 8½ in) folded in thirds ends up the same size with half the bulk, so it is the neater choice for a note sent with a check.

#6¾, #9 or #10: which to choose

The #10 envelope is the standard US business envelope, much longer and a little taller than the #6¾, and it is built around a Letter sheet folded in thirds. The #9 envelope is just small enough to travel inside a #10 as a reply envelope while still taking that tri-folded sheet. A #6¾ fits inside either of them, which is why it works as an enclosure too.

So the choice depends on what has to come back. If your customer returns only a check and a payment slip, a #6¾ is enough and adds the least bulk to your mailing. If they also return a signed form or a full Letter page, enclose a #9 instead, and send your own invoices and letters in a #10.

Printing the address at home

Most home printers take a #6¾ through the rear slot, the manual feed or the multipurpose tray, usually short edge first, and the manual or the icon by the tray shows which side faces up and where the flap goes. What can stop a small envelope is the printer's minimum paper size, so if your manual gives a minimum width, compare it with this envelope's short side before you buy a box. In the print dialog, pick the envelope size or a matching custom size and print at 100% so the address isn't shrunk or shifted. On a laser printer the heat can stick a gummed flap down, so test one envelope first.

The button on this page opens the label editor at the #6¾ size, with a return address block top left, a recipient block in the middle and the stamp corner left free. From there you export a PDF that is exactly the envelope's size, or print straight from the browser. For a stack of reply envelopes, type your own address into the recipient block, delete the sender block and set the number of copies in the print dialog. If your printer won't take envelopes this small, you can print address labels on a US Letter sheet (Avery® 5160 size, 30 per sheet) instead, and the guide to printing envelopes covers test prints and feeding in more detail.

Postage in the US and the UK

In the US, a #6¾ is mailed as a First-Class Mail letter, not as a large envelope. Up to 11½ × 6⅛ in, ¼ in thick, 3.5 oz: that is how USPS defines a letter, and this envelope sits well inside those limits as long as it stays flat. A check, a slip and the envelope weigh only a few grams, which keeps it in the lowest weight step, so one Forever stamp, the everyday First-Class stamp, covers it; current prices are on the US stamp prices page.

In the UK the size is rarely sold, because offices there use ISO envelopes such as the DL, but a #6¾ posted there counts as a Letter, not a Large Letter. Up to 24 × 16.5 cm, 5 mm thick, 100 g is the limit for a Royal Mail Letter at both 1st and 2nd Class, and a #6¾ is far inside it. One 1st or 2nd Class stamp therefore covers it, unless you pack it thicker than the limit allows, which a check and a short note never will.