How much electricity does the average American household use in watt hours?

About 1.3 kWh/hour.

According to EIA, 2010 average electricity use per household: 11496 kwh/yr

Hours in a year consisting of 365 days x 24 hours a day: 8760 hrs/yr

Dividing annual average figure by total hours in a year: 1.312328767 kWh/hr