Determining the Fractional Scale of a Map or Scale Model

The fractional scale of a scale model is the ratio between two sets of
dimensions (as between those of a model car and its equivalent actual
car). The formula for determining the fractional scale of a map or scale
model is:

          1
Scale = _____
        AS/MS

Where:
   1 = In a fractional scale, the numerator is always "1"
  AS = Actual Size
  MS = Equivalent Model Size

"AS" and "MS" should be in the same units, e.g., cm, so that the units 
will cancel.

Example: If a model car is 20cm long, and the actual car is 3m long, then 
what is the scale of the model car?

Step 1. Convert meters to centimeters:

          3m = 300cm

Step 2. Calculate scale:

              1
          __________ = 1/15
          300cm/20cm

Therefore, one unit on the model is equivalent to 15 of the same units in
the real world. Every feature on the model is 1/15 of actual size; every
feature on the actual car is 15 times larger than the same model feature.