does screw length include the part of the screw that is in the nut?

I need a tool to measure the length of a screw. I would normally say,
use a ruler. But my local DIY stores don't sell them, and the rulers
that stationary shops sell are no good because the 0 is not in line
with the end of it. I don't really want to get one of theirs and file
it down.
A micrometer would measure screw length including the nut, but not
excluding it.

How should i measure it, what product should i use and who sells it?!