"Around" being the operative word. Measure the length of 10 different saddles and you get varying results depending on brand and model. Average the length of 10 different mens saddles and you get 10.5". That is likely the value of the constant that the fit computer is using to come up with its results as you enter your various parameters into its formula. And no, the formula won't work for all road bikes, only the ones that have the same exact length of seat and top tube, and stem, etc. that will be recommended when the calculator spits out its results.