The kWh math every homeowner should know

The plain-language definition

A kilowatt-hour is the energy used by a 1,000-watt appliance running for one hour. That is it. The unit is energy, not power. Power is the instantaneous draw (how hard the appliance is working right now); energy is power times time (how much work was done over a period).

Your bill measures energy because that is what you pay for. Your meter integrates power draw across time and totals it as kWh consumed in the billing period. Multiply by your supply rate (cents per kWh) and you get the supply portion of your bill.

The average US household uses 877 kWh per month

EIA Form-861 panel data puts the average US residential customer at 877 kWh per month. That is 10,500 kWh per year. At an average residential supply rate of 16 cents per kWh, the supply portion of the bill averages $140 a month before delivery, capacity, taxes, and riders.

The state-by-state range is wide. Louisiana leads at 1,250 kWh per month (high cooling load). California trails at 540 kWh per month (mild climate, high rates incentivise conservation). The driver is mostly climate, not behaviour.

kWh per appliance — the lookup table

Central air conditioner: 3 to 5 kW draw, runs 4 to 8 hours per day in summer, total 12 to 40 kWh per day. Roughly 360 to 1,200 kWh per month during peak cooling.

Electric resistance water heater: 4.5 kW draw, runs 3 to 5 hours per day, total 14 to 22 kWh per day. Roughly 420 to 660 kWh per month.

Refrigerator (modern ENERGY STAR): 50 to 60 kWh per month continuous.

Clothes dryer (electric): 4 to 6 kWh per load.

Oven: 2 to 3 kWh per hour of use.

LED lightbulb (10W): 0.01 kWh per hour of use.

Phone charger (5W): 0.005 kWh per hour. Often less than 0.5 kWh per month total.

Reading the kWh number on your bill

Every US electric bill prints the kWh consumed in the current billing period. Find the line labelled Total kWh, Usage, or Consumption. The supply portion of the bill is that number times your supply rate.

Some bills break out kWh into time-of-use buckets (peak, mid-peak, off-peak). On those bills you have multiple supply rates, and the total supply portion is the sum of (kWh in bucket) times (rate for that bucket). Time-of-use math is covered in the dedicated post on TOU rates.

Watts vs kilowatts vs kilowatt-hours — the common confusion

Watts and kilowatts measure power (the rate of energy use right now). Kilowatt-hours measure energy (power times time). A 60-watt LED bulb is drawing 60 watts whenever it is on. Run it for an hour and it has used 0.06 kWh. Run it for 16.67 hours and it has used 1 kWh.

Your supply rate is denominated in cents per kWh, not cents per watt or cents per kilowatt. Your meter measures kWh, not watts. The watts number is useful for understanding individual appliances; the kWh number is what you actually pay for.