[Nater11]

Ok so here goes:

I'm going from 25.5 mg to g.

25.5 mg |  10^-3 | 1 g
            |  1 mg|  ?


So what number do i plug into that? I've got a conversion chart and everything, but im not sure what to put for the base unit... I thought it would just be "10". is that right?

[Borek]

You are converting miligrams to grams. What does "mili" stand for?

[Yggdrasil]

The conversion should look like:

25.5mg * (10^-3g/mg) = 0.0255 g

Since 1 mg = 10^-3 g.

[enahs]

Or:
25.5 mg * (   1g     ) =
               1000mg

[constant thinker]

Yggdrasil is completely right, but I find personally enah's way is easier to understand. When I've taught people about converting, I usually teach them using the way enahs posted (multiply by a fraction and cancel out units).

Nater11, if you aren't sure about how to convert something in the future try doing things the way enahs did it. The fraction is simply a conversion factor. In this case 1g = 1000mg. You want to convert to g so you need mg on the bottom to cancel out. Therefore you need to use
(  1g  )
1000mg                  like enahs did.