Electricity usage is measured in kilowatt-hours (kWh), which is the amount of energy used by an appliance over time. Your bill usually shows the billing period, total kWh used, usage charges, supply charges and any discounts or credits. Heating, cooling, hot water systems, dryers and older appliances can use more electricity, so checking their running time and energy ratings can help explain changes in usage. You can compare bills or check your smart meter data, and contact your electricity retailer if a reading or charge seems unclear.