Your electric bill is measured in kilowatt-hours, but appliance labels show watts or amps. Once you know how these connect, you can work out what any device costs to run and where your money really goes.

Watts vs. kilowatt-hours

• Watts (W) measure how much power a device draws at a given moment.
• Kilowatt-hours (kWh) measure energy used over time: 1,000 watts for one hour.

Think of watts as the speed and kWh as the distance. A 100-watt TV running for 10 hours uses 1 kWh, the same as a 1,000-watt microwave running for one hour.

The formula

kWh = watts × hours ÷ 1,000
cost = kWh × your rate per kWh

If the label shows amps instead:
watts ≈ volts × amps   (e.g. 120 V × 5 A = 600 W)

The Electricity Cost Calculator does this for you and shows the cost per day, month and year.

Why labels can overstate real use

The wattage on a label is usually the maximum. Many appliances don’t run at full power all the time:

• Refrigerators, air conditioners and heaters cycle on and off with their thermostat.
• Computers and TVs draw less when idle or dimmed.
• Washers and dishwashers use the most power while heating water.

For large appliances, the yellow EnergyGuide label lists estimated yearly energy use in kWh, which is more realistic than the nameplate wattage.

Measure instead of guessing

A plug-in energy usage meter sits between the outlet and the device and records actual kWh over days or weeks. It’s the easiest way to find out what a fridge, freezer or gaming PC really uses. Many utilities also show hourly usage in their app or online account.

Where the energy usually goes

In most homes, the largest users are the ones that make heat or remove it: space heating and cooling, water heating, clothes dryers and electric cooking. Lighting and electronics matter less individually but add up. That makes heating, cooling and hot water the best places to look for savings. For portable heaters specifically, see what a space heater costs to run.

Key takeaways

• kWh = watts × hours ÷ 1,000; multiply by your rate for the cost.
• Nameplate watts are a maximum; real use is often lower.
• Focus savings on heating, cooling and hot water.