Your electric utility bill probably shows your energy use for the month in units of kilowatt-hours. A kilowatt-hour is defined as the energy used in 1 hour at a rate of 1 kilowatt (1,000 watts); that is, 1 kilowatt-hour = 1 kilowatt × 1 hour.
If your bill says you used 800 kilowatt-hours, how much energy did you use in joules?