How do blender units convert to regular units like centimeters for creating realistic models to scale and such?
“regular units” don’t exist in Unity. Scale it however you want, but there’s no reason you should scale anything. A unit means whatever you want it to.
I’m not talking about just Unity. Is there anyway to use regular measurements in blender?
Blender has a decimal Unitsystem and Unity too,
like Jessy said you can make a unit 1 Centimeter/Meter/Kilometer …
So it´s up to You what messurement you use, but there´s a plugin for Blender that maybe can help you 
http://www.blendercookie.com/2010/01/13/measuring-objects-and-distances-in-blender/
what he means is ‘what does one blender unit translate to in unity units’
Which I believe it’s just 1-1.
That’s not what I mean… GameGuy, thank you.
the scale Rait for Unity and blender is 1:1, Blender 2.5 allready has the Measurement feature, go to mesh display in the side bar, then check the FaceArea, Edge length boxes. and Face Angles if you wish.
Blender units default to meters, so does unity. So, 1 unit is the same in both, and should scale just fine.