I swear you could do this in MS Paint and Irfanview in the past, but I can't figure it out.

I've got an image of a part which I need to print in the actual size of the object, I can use my laser printer and make it a 4 sheet
image or take it to Staples and have them print it on 1 sheet.

Where I'm hung up is that I put a 12" ruler in the image, and I need to size the image so 12" = 12" when printed.

I seem to remeber that you just drew a line on the ruler in the image and resized that line to 12" in inches (rather than pixels
or ratio of whatever.)

Any help?