In a recent thread in Apple Aperture Discussions Show sizes in inches the OP wanted to have Aperture display the size of the image in inches. The only problem with the request is that an images doesn't have a size until the pixels meet the paper.

That discussion led to this Aperture service. It will take the current selection and return the size in inches of the image at a DPI of your choosing. It defaults to 300 dpi but you can enter a different dpi.

To install download and uncompress then copy it into ~/Library/Services then restart Aperture. To examine it open in Automator.