A scale factor is a number which scales, or multiplies, some quantity.
In the equation y = Cx, C is the scale factor for x. C is also the coefficient of x, and may be called the constant of proportionality of y to x.
For example, doubling distances corresponds to a scale factor of 2 for distance, while cutting a cake in half results in pieces with a scale factor of ½.
http://www.ixl.com/math/grade-7/scale-drawings-and-scale-factors
This is the IXL 7th grade target J.13 Scale Drawings and Scale Factors. Perfect practice for Lessons 17, 18, and 19 of the 7th grade common core.