How long do you need to stay in the sun to get a tan?

Many people assume that it has a lot to do with the temperature but usually the temperature is only an indicator of what the UVB levels are at. The hotter it is the more UVB that day (UVB is what causes skin cancer, causes you to burn & tan). I would say though since many people don't know how to measure UVB levels that 85 degrees is a good tanning temperature (with little or no clouds)