Learn the melting point of solder from expert Jeff Koskulics in this Howcast video.
The melting point of solder depends upon its particular formulation. In the case of eutectic tin-lead solder, the melting temperature is somewhere around 360 degrees Fahrenheit. The temperature becomes a bit higher with different formulations of solder, such as 60/40 tin lead, which may be 10 degrees higher. Higher temperatures can also be expected for lead-free versions of solder, and that may change the temperature at which you’d want to use for your soldering iron.
Your soldering iron obviously has to be much hotter than the particular material you’re trying to melt. The heat has to flow from the tip to the work piece so that it can melt the material. So we typically have a setting of temperature that is hundreds of degrees hotter, so that the material can heat rapidly, melt efficiently, and proceed very quickly.
So for typical solder work, I usually use temperatures between 650 and 700 degrees Fahrenheit. You may expect hotter temperatures for very heavy or large work pieces, and perhaps higher temperatures for lead-free solders.