If you're looking to convert rft measurements into sq ft, you'll be disappointed to hear that there is NO WAY to do this.
Let's take a look at why:
What you need to remember is exactly what these measurements stand for.
An RFT is actually a "Running Foot" - which is a one dimensional unit of measurement
SFT on the other hand is what is known as a Square Foot - a measurement of area that has both length and width: Thus making it two-dimensional.
Because they are different types of measurement, they can't actually be compared. It'd be like comparing the length of a line segment to the area of a square: Impossible!
However, if you're interested in working out conversions of square feet, then I CAN recommend the following website: http://www.metric-conversions.org/area/square-feet-conversion.htm