The two settings that matter
Scale must be Actual Size or 100 percent. Anything else resizes the routing barcode and the postage indicium. Barcodes encode data in bar widths, so a label printed at 96 percent can fail to scan even though it looks fine.
Paper size must match the physical thing in the tray. If you are feeding a #10 envelope, the driver needs to say Envelope Com 10. If it says Letter while an envelope is loaded, the driver lays the job out for a sheet of paper and the envelope catches whatever part of it happens to pass under the head.
Where each app hides them
| App | Set scale to | Set paper size in |
|---|---|---|
| Chrome / Edge | More settings, then Scale: Default is wrong. Choose Custom: 100 | Print using system dialog, then printer Preferences |
| Adobe Acrobat Reader | Page Sizing & Handling, then Actual size | Page Setup, or the Properties button next to the printer |
| macOS Preview | Scale: 100%, with Auto Rotate off | Paper Size dropdown in the print sheet |
| Firefox | Scale: 100 rather than Fit to page width | Print using the system dialog |
| Windows Photos / built-in viewer | Not reliably exposed. Use another viewer | Not reliably exposed |
The Chrome row is the one that catches people. Chrome defaults to fitting the page to the printable area, which is a form of scaling even when it does not call itself that, and its built-in dialog often will not offer envelope media at all. Click Print using system dialog to reach the real driver.
Settings on the printer side
Inkjet and laser printing directly onto envelopes
- Paper size: Envelope Com 10, sometimes listed as #10, Com-10, or 4.125 x 9.5 in.
- Media type: Envelope. This slows the paper path and adjusts ink density, and on laser printers it raises fuser temperature so the glue does not soften.
- Feed orientation: match what the driver diagram shows to how the envelope physically sits against the tray guides. Getting this wrong flips the design 180 degrees.
- Two-sided printing: off.
- Borderless or edge-to-edge: off, since it shifts the whole image inward to guarantee bleed.
- Feed one envelope at a time if your tray allows it, because envelope stacks skew easily.
Thermal label printers producing a 4 by 6 label
- Media: 4 x 6 in, also listed as 100 x 150 mm.
- Resolution: 203 dpi on most models, 300 dpi if yours supports it. A mismatch here shows up as a subtly stretched label.
- Driver: install the vendor driver for your Zebra, Rollo, DYMO, or Brother unit rather than a generic class driver, which frequently gets the media size wrong.
- Orientation: portrait.
- Darkness and speed: raise darkness a step if barcodes look grey or feathered on a scan test.
A thermal printer cannot feed a #10 envelope, so if that is your printer the 4 by 6 output is the right choice. Use the converter to recover a clean 4 by 6 label from a letter-size PDF, print it on label stock, and apply it by hand.
Confirming the print is really 1:1
Print dialogs will happily report Actual Size while a driver-level setting quietly rescales the job. The only reliable check is physical.
- 1Print one copy onto plain paper at your chosen settings.
- 2Measure the routing barcode across its full width with a ruler.
- 3Open the original eBay PDF and measure the same barcode on screen at 100 percent zoom, or print it separately at Actual Size and measure that.
- 4If the two measurements differ, something in the chain is scaling. Work backward through the print dialog, then the driver Preferences, then any printer front-panel scaling option.
Settings that look helpful and are not
- Fit to Page, Shrink Oversized Pages, and Scale to Fit all resize barcodes. Leave them off.
- Auto Rotate and Center is fine on a page that already matches the envelope, and actively harmful on one that does not, since it is what centers the label in the first place.
- Draft or Economy mode saves ink by thinning coverage, which is exactly what makes a barcode fail to scan.
- Booklet, multiple pages per sheet, and poster modes all rescale. None belong here.
If the label is still landing in the middle of the envelope after all of this, the problem is the page size rather than the settings. The guide on centered labels explains why, and the dimension reference lists the exact page sizes involved.