How accurate are you trying to get?
A big part of this is knowing the limits of the sensor. In any case the sensor should have a product code of some sort on it. You can google this to find the data sheet and see what the limits are. Then you can adjust your code accordingly.
If you haven't already then check out this beginner's guide. Project 13 covers Serial Temperature Sensors. It will show you how to go about writing the code to get the proper readings.
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