This Java applet computes alcohol-by-weight (ABW) and alcohol-by-volume (ABV) given the specific gravity (Original Gravity) and temperature of the "green" beer and the specific gravity (Final Gravity) and temperature of the finished beer.
Since temperature effects specific gravity of a liquid, this must be taken into account when measuring gravities of beer and wort. The benchmark temperature is 60 degrees fahrenheit. Any deviation from this requires adjustment. This calculator performs this adjustment based on the Hydrometer Correction tables in The Home Brewer's Companion, by Charlie Papazian and the The Brewer's Companion by Randy Mosher.