To calculate the amount of energy needed to boil the water you need to know 3 things: the mass of the water (m) in kg; the increase in the water's temperature (∆θ) in degrees Celcius; the specific heat capacity (c) in joules per kilogram per degree celcius. The specific heat capacity is the amount of energy required to raise the temperature of kilogram of a.substance by one degree Celcius, and for water it is equal to 4,200 J/kg/°C.