Safari uses the printer settings in Mac OS X to determine which printer and paper size settings are used. Because Mac OS X print paper sizes are set to US Letter format by default, it may be necessary to adjust the print settings for Mac OS X, if your labels are not printing the correct size.
Note: Mac OS X 10.6 and earlier will not let you set a custom default print size.
Mac OS X Printer settings
In Safari press Command ? + P keys to open the Print Dialog window.
Click the menu next to Paper Size, then select Manage custom sizes.
Click the "+" sign (bottom left) to create a new paper size.
Change the name by double-clicking on "Untitled". We recommend changing the name to something you will remember, such as "4x6".
Leave the "Non-Printable Area" set to "User Defined" and change the margins if necessary - we suggest a very small margin or no margin.
Click “OK” to return to the print dialogue box.
Back on the Print Dialog screen, click "Cancel".
Navigate to System Preferences on your Mac.
Click on "Printers & Scanners".
Set the default paper size to the 4x6 template you just created, by selecting the name you assigned it. You can also set the default printer if you prefer.
Return to Safari and press the Command ? + P keys to open the Print Dialog window.
Next, click the Print button to print your labels.