http://www.csgnetwork.com/tempconvjava.html
http://www.teaching-english-in-japan.net/conversion/celsius
ps. Temperature is not a logarithmic scale; it is linear.
EDIT: Oops, didn't mean to bump this silliness.
Same thing. If you just think of Fahrenheit as a yardstick that has the "0" somewhere in the middle, you can see why you have to use Kelvins in order to get a true measure of "twice as much heat".