The Boil Off Calculator is actually two calculators in one. It is both a Boil Off Calculator and an Evaporation Rate Calculator.

The Calculator will let you determine the gravity of a wort when a given amount is evaporated off, and also let you determine the evaporation rate. The Calculator will allow you to use a variety of methods, from using an evaporation rate in percentage or volume by hour to free-form evaporation rate entry.