Going back to Formula 2, calculation of the thermal contact conductance may prove difficult, even impossible, due to the difficulty in measuring the contact area,  (A product of surface characteristics, as explained earlier). Because of this, contact conductance/resistance is usually found experimentally, by using a standard apparatus.
The results of such experiments are usually published in Engineering literature, on journals such as [http://scitation.aip.org/ASMEJournals/HeatTransfer/ Journal of Heat Transfer], [http://www.elsevier.com/wps/find/journaldescription.cws_home/210/description#description International Journal of Heat and Mass Transfer], etc. Unfortunately, a centralized database of contact conductance coefficients does not exist, a situation which sometimes causes companies to use outdated, irrelevant data, or not taking contact conductance as a consideration at all.
[http://sourceforge.net/projects/cocoe/ CoCoE] (Contact Conductance Estimator), a project founded to solve this problem and create a centralized database of contact conductance data and a computer program that uses it, was started in 2006.