I am looking to take a 3D model from the warehouse and scale it from full size to a scale, i.e. 1’=1/4" or 1:48. I have been successful so far in using the tape measure tool with models I have drafted myself (reference line at 1’, re-size model so 1’=1/4") but this does not work with imported images. I have figured out the scale tool as so far as typing .5 while scaling will scale the model to half it’s size, and so on. However, I cannot wrap my head around the number to type in to get the desired ratio scale. Because it’s not the percentage of 1’, it’s of the entire model.

Just do the math, Either take overall size or just pick a line.
Example: if overall model is say 24’ and you want it down to 18":
1.5’/24 = 0.0625
Scale your drawing to 0.0625 and you get:
1’=0.75"(3/4")

But the issue is that I don’t know that I want 18"; I don’t know the overall desired size. I know I want every 1’ to equal 1/4". I need to know how to get to the starting point of that calculation, or to go another route.

You’ve downloaded the model you want right? Once you’ve downloaded the model, just measure an edge or draw a 12" line. You can use that as a reference to scale everything down to whatever size you want.

-Download the model
-Draw a 12" line
-Measure that 12" line
-Type in the size you want it to be (example 4")
-The model should then tell you that it’ll scale everything down, accept.

She could explode the component and any nested inside.
Whether that option is attractive or not depends upon the modeling situation.

One could open the component for editing and then use the Tape Measure to scale the active group.
But if there happen to be components nested inside; they will not be scaled.
You’ll get this…

One would need to scale those from within their editing context as well.
It’s quicker and easier to use the Scale tool.