Try to print something in Preview and it’ll always scale it to fit the page. This can be ridiculous sometimes if you’re trying to print a small resolution photo — you’ll end up with output that looks blocky and ugly.
You can deactivate scaling in the print dialog box — just click the Scale radio box, and type 100% — but this isn’t remembered each time Preview starts, so you must do it each time.
The solution is to quit Preview if it’s open, then open a Terminal window (you’ll find Terminal in the Utilities folder of the Applications list of Finder) and then type the following:
defaults write com.apple.Preview PVImagePrintingScaleMode -bool FALSE
From now on Preview’s Scale radio box will be automatically selected with a value of 100% automatically entered. Bear in mind that this can be a hindrance if printing a picture or PDF that’s larger than the page because you’ll end-up only printing part of it. However, you can always enter a smaller value into the scale percentage box to ensure it fits.
To revert back to default scaling settings at a later date, again quit Preview and open a Terminal window before typing the following:
defaults delete com.apple.Preview PVImagePrintingScaleMode