Four ways, from free to about $25

1. The nameplate (free, maximum draw)

Every appliance has a plate or sticker, usually on the back, the bottom or the power brick, listing its electrical rating. Look for a figure in watts (W). If there is only amps (A), multiply by volts: 120 V for a normal outlet, 240 V for a dryer or range outlet. Some labels list volt-amps (VA), which for household purposes you can treat as watts.

The nameplate is exact for resistive appliances that are either on or off: kettles, toasters, incandescent bulbs, hair dryers, space heaters on high. For everything else it is a ceiling. A microwave labeled 1,500 W input delivers about 1,000 W of cooking power. A refrigerator labeled 700 W averages 60. A laptop charger labeled 65 W draws 65 W only while the battery is low and the CPU is busy.

2. The EnergyGuide label (free, tested annual use)

Refrigerators, freezers, dishwashers, clothes washers, water heaters, room and central air conditioners, furnaces, pool heaters and televisions sold in the US carry the yellow EnergyGuide label. It shows an estimated kWh per year under a standard federal test, alongside the range for similar models.

For appliances that cycle, this is far better than the nameplate. Enter it in the calculator's "I know the kWh" mode and you are done. If the label is long gone, search the model number (on a sticker inside the door or on the back) with "EnergyGuide" or "ENERGY STAR"; the manufacturer's spec page or the ENERGY STAR product finder will have the figure.

Two limits. The test assumes typical use, so a fridge in a hot garage or a dishwasher run twice a day will use more. And a label from 2008 tells you what the appliance used in 2008; seals wear, coils clog and compressors lose efficiency.

3. A plug-in power meter (about $25, real measurement)

This is the tool that turns guessing into knowing for anything with a normal plug. Plug the meter into the wall, plug the appliance into the meter, and read the display.

What to look at:

  • Watts right now. Watch it change as the appliance does different things: a fridge compressor starting, a TV going from dark scenes to bright, a PC launching a game. This is the number that will surprise you most.
  • kWh accumulated since you plugged it in, and the elapsed time. Divide one by the other for average kWh per hour or per day. This is the number to use for cost.
  • Standby watts with the appliance switched off but still plugged in. Anything above 1 or 2 W is worth noting; see the phantom load guide.

How long to leave it:

  • Kettles, toasters, hair dryers, microwaves: one use is enough. Note the kWh per use.
  • TVs, computers, consoles: a typical evening.
  • Refrigerators, freezers, dehumidifiers, aquariums, anything with a thermostat: a full week. Daily cycles, defrost heaters and door openings all average out over that period.
  • Washers and dryers (120 V compact models): one full cycle each.

Some meters let you enter your rate and show cost directly; you can also type the measured watts or kWh into the electricity cost calculator to scale it to a month and a year at your rate.

4. Your smart meter or a panel monitor (free to $150, whole house and 240 V loads)

A plug-in meter cannot measure a 240 V appliance, hardwired equipment such as a furnace blower or water heater, or the house as a whole. For those:

  • Utility interval data. Log in to your utility account and find the hourly usage graph. To isolate one appliance, pick a quiet hour, run only that appliance, and compare the reading with the hour before. This works well for a water heater reheat, a dryer load or an EV charging session.
  • The meter itself. Older smart meters have a small "current demand" readout on the display; watch it while switching a load on and off.
  • A panel monitor. Devices such as the Emporia Vue or Sense clip current sensors onto the wires in the breaker panel and report every circuit in an app. Installation involves opening the panel, so it is an electrician's job unless you are comfortable with that. For a home with a heat pump, EV and electric water heater, it is the only way to see all the big loads at once.
  • The appliance's own reporting. Smart EV chargers, most EVs, many heat pump thermostats and some water heaters report their own kWh use in their apps, and they are generally accurate.

What the measurements usually show

After measuring a few hundred household appliances, a few patterns repeat:

  • Old refrigerators are the biggest surprise, often at two to three times their original label figure.
  • Space heaters with a thermostat cycle far more than people expect in a small closed room, and far less than expected in an open one.
  • Desktop PCs and gaming consoles idle high. A machine "doing nothing" at 80 to 120 W is common.
  • Modern TVs, LED lighting and phone chargers are barely worth measuring. The numbers are small at every hour of the day.
  • Anything with a heating element and a timer (coffee makers with a hot plate, towel warmers, heated floors) uses more than its owners assume, because the element runs far longer than the "use" does.

Once you have real numbers, the wattage chart is a good sanity check, and the most expensive appliances guide tells you which measurements are worth acting on.