A little setup on Google Sheets and you can print barcodes (along with whatever else you want) onto label sheets WITHOUT messing with mailmerges or barcode fonts that make unreadable barcodes!
UPDATE: It looks like enough people were using these types of sites for this that many of them have monetized when you try to do more than a certain number. Good for them - why shouldn't they make a little money off of their own hard work?! A few of these of have come and gone, or changed their setup since I first made this. Just recognize that, by the time you look into this, you may need to find a different website for barcode creation, or potentially pay some money to the web service if you need to do large numbers.
I spent weeks printing barcodes using a mail merge with Excel and Word, converting numbers to barcodes using a barcode font. There are a few big problems with this. First, mail merges take some time to set up EVERY SINGLE TIME. Second, Microsoft Word has formatting characters that are invisible in normal fonts but become visible in barcode fonts, making the barcodes unreadable. Getting rid of those invisible characters requires some sneaky tactics, not to mention the need for particular special characters to start and end the data being turned into a barcode. Third, sharing files created that way is a pain because everyone you share it with has to download the same font you had to make it readable, or you have send a pdf which isn't editable. Fourth, barcode fonts are limited to codes that convert one character at a time, so something like a QR code can't be generated with a special font.
This method avoids all of those problems - no mail merge, no barcode fonts, and the versatility to use whatever barcode (or QR code) type you want.
This makes use of online barcode generator sites and the Google Sheets "IMAGE()" function. Effectively, you are outsourcing the actual code creation to a website that somebody else already made and bringing back an image file, so you won't have to mess with anything to get the barcode to read correctly!
Here's the link to the file I made - feel free to make a copy and use it for your labels. It might take a little adjustment to get it to print correctly with your printer, but all the formulas for either barcodes or QR codes are already done.
docs.google.com/spreadsheets/...