A shipping label works when it lies flat on one side of the package, is not folded over an edge, and is the only readable label and barcode on the box. USPS accepts a label printed on regular printer paper and attached with clear packing tape, and a participating Post Office can print one from a QR code.
Those rules are from the USPS Preparing Packages guide. For what each part of a label means, see the shipping label glossary entry. This post covers the part that goes wrong at the packing table.
Where a shipping label goes on the box
USPS gives four placement rules, and each one exists because the package is read by machines before a person ever looks at it:
- One side only. USPS says to “put all labels on the same side, and don’t fold them, bend them over edges, or overlap them.”
- The long side. The USPS Postage Verification page says to place the label on the long side of the package and keep it off edges and corners.
- Barcodes facing one way. The same page asks that all barcodes face the same direction.
- Addresses parallel to the longest side. For a handwritten or separately printed address, USPS wants it parallel to the longest side, with the return address, delivery address, and postage all on the same face.
If the box is too small for the label to sit flat on any side, the box is the problem, not the label. A label wrapped around a corner splits its barcode across two planes.
Printing a shipping label: plain paper is allowed
USPS states that you can print a label on your own printer using “regular printer paper,” and then “just tape the printed label to your package with clear packing tape.” A thermal printer and adhesive label stock save time, but neither is a requirement. The thermal printer post covers when the upgrade is worth it.
Three habits prevent most print problems:
- Print at actual size. A label file is laid out for a specific size, usually 4 by 6 inches. “Fit to page” or “shrink to fit” rescales the barcode along with everything else.
- Print one label per package and use it once. Every label carries its own tracking number.
- Look at the barcode before you tape. If a line of the print is faded or streaked through the bars, reprint it.
Reusing a box: cover everything old
A reused box is fine with USPS, with two cautions from the Preparing Packages guide. Boxes weaken in shipping, so check that it is still sturdy. And “make sure all old logos, barcodes, shipping labels, and addresses are covered or blacked out.”
UPS gives the same instruction in the packaging section of its Rate and Service Guide: remove or conceal any labels, hazardous materials indicators, and other previous shipment markings that no longer apply. A sorting machine cannot tell which barcode is the current one.
Old hazardous-material markings are the ones to be most careful about, because they describe contents the box no longer holds. Can You Ship That? covers the reused-box trap in more detail.
The label has to match the package it is on
A label is a statement of what you are shipping: the service, the weight, the size, and where it starts. USPS checks those statements by machine, and a mismatch becomes a postage adjustment after the fact. Four matches to confirm before you tape:
| What the label says | What has to be true |
|---|---|
| Service | The packaging belongs to that service. USPS lists a label whose service does not match the packaging as a common discrepancy. |
| Weight | It is the weight of the sealed package, including packing materials, rounded up. USPS says to weigh on a kitchen or postal scale, not a bathroom scale. |
| Dimensions | They are the outside measurements of the box you actually used. |
| Ship-from address | It is where the package actually enters the mail. USPS prices by zone, and tells senders using postage software to verify that the sender’s address is up to date before printing the label. |
The post on USPS adjustments covers what happens when one of these is off and how to dispute a wrong charge.
Closing the box so the label survives
A label is only as secure as the surface under it. USPS recommends enough 2-inch-wide packing tape to close and secure all seams, and says not to wrap a box in string, cord, or twine, which catches in sorting equipment.
UPS adds one inexpensive safeguard in its packaging guidelines: place a duplicate address label inside the package. If the outside label is torn off, the package can still be identified.
No printer: three ways to get a shipping label on the box
USPS Label Broker. When a label is paid for online and set to print later at the Post Office, USPS issues a Label Broker ID with a QR code. USPS says you can take the sealed package and the code to a participating Post Office and have the label printed at the counter for free (Label Broker). Some locations have a self-service kiosk that does the same. A store or ecommerce platform can also issue a Label Broker ID and send it to you by email or text.
USPS Label Delivery. For labels created in Click-N-Ship, USPS will print the label and deliver it to you for $1.65 per label, according to the same Label Broker page.
Someone else’s printer. A label is a PDF. It can be saved on your phone and printed anywhere that prints a document, at actual size. Generating shipping labels from your phone walks through that.
A 20-second check before the package leaves
- The label is flat on one side, not over a seam, edge, or corner.
- No other barcode, address, or old marking is visible anywhere on the box.
- The service on the label matches the packaging.
- The weight and dimensions on the label are the sealed package’s, not the product’s.
- The tracking number is saved with the order.
Sources
Checked October 12, 2026 against USPS Preparing Packages, USPS Postage Verification, USPS Label Broker, and the packaging guidelines in the UPS Rate and Service Guide, 2026 edition (updated September 7, 2026).
Related Topics
- Shipping label created: what that tracking status means and how long it lasts
- Do you need a USPS SCAN Form? for handing over many labeled packages at once
- Why USPS tracking numbers start with 9
- Packaging best practices