How do I calculate what is a fair interest rate to apply to a personal loan?

Is 10% a fair rate to apply to a personal loan originating in the U.S. ? How about if it originated internationally?How do I calculate what is a fair interest rate to apply to a personal loan?
In the US, the prime is 8.25%. The rates right now for any lending in the US is pretty bad because of our economy. Check http://www.bloomberg.com for more info on rates and exchanges nationally and internationally. But 10% in the us is pretty good. Rates are between 7-22% right now, depending on reserves you have (stocks and savings) and credit rating. A credit union will ususally have a lower rate, though. If it's an auto loan, shop the dealers for finance specials, and if you own a home, a home equity (HELOC) is the best way to finance anything (besides cash), because the rates are usually lower.How do I calculate what is a fair interest rate to apply to a personal loan?
I would see what the prime rate is and check with some banks to see how much they are charging for personal loans and go from there. However, if you are making a loan to a person because they can't get one at a bank then charge whatever you want and they will probably pay it.