I have seen basic calculators on the web that help you make estimates. Check the sticky threads above. The publishers of Model Airplane News have a book called the "Basics of R/C Model Aircraft Design" which has 4 or 5 chapters explaining the details of finding your answer. The book has a lot of engineering formulas, but just reading the explanations are informative. Just to indicate how complicated an accurate answer is ... turbulent airflow from fuselage or downwash from another surface can ruin any paper calculations. Since I have very limited skills with mathematical formulas, I prefer to experiment with a model. I built extra large surfaces and cut them down to as flight testing indicated.