n/a

They measure related things differently so I am not aware of any way to convert one to another. 90.1 Appendix A contains some guidance for how to model some assemblies if the software does not directly take F or C Factors.

App. A is rather inflexable with other methods for calculating F-factor u-values and specifically states that you can't. For example, you can't use a 2/3d FEM program in this case. The engineering reference for energyplus describes how the program "reverse engineers" an equivalent construction with concrete and insulation from the user F & C factor inputs. You'll find the pdf with google. It's a big document so you'll search for C-Factor and F-factor to find the right section. Several factors play a role...depth of wall, perimeter of slab, etc. But that's not all. The appropriate boundry conditions have to be applied to the "exterior" side of the element also during simulation. I made a slightly more detailed post regarding F-factors some time ago.

USGBC allows the following if the software does not model F-factor, model the Baseline slab-on-grade floor as a six inch concrete slab over earth with a soil conductivity of 0.75 Btu/h-ft-°F in accordance with A6.1.