Using a ruler

Maybe this is obvious, but I've only recently been using it a lot. This example was used for a cover up, but I use it even more when I'm planning a tattoo for a certain space.

All I do is hold up a ruler to the piece when I take a picture. That's it.

After transferring the images to my computer, I open up Photoshop.
Create a new file (File > New). For a new document I always use the Photoshop Preset: U.S. Paper. (Size - Letter) This creates a standard 8.5" by 11" sheet at a 300 dots per inch resolution.

Next, I open the image I want and drag it onto the new document. Making sure the rulers are showing (View - Rulers) I click on the ruler and drag/pull a guide down to the inch mark. And I drag another down to the two inch mark.

Then it's a matter of resizing the photo; enlarging or reducing enough so the inch and two inch marks line up with the guides.

Pretty easy.

Then I have my size. Sometimes I print it out and draw over it. Other times I use my Wacom and sketch right there. It's perfect. And it helps with figuring out sizing for cover ups.

I also have paper rulers I print out and use as well. I like using a new one for every person, so I just print them out and throw them away. It's nothing special, but, when I get time, I'll throw it in the reference section so it's easy to just grab and print.