Choose a meter that fits the appliance
Watts (W) show how quickly a device uses electricity at a particular moment. Kilowatt-hours (kWh) show how much it used over a period. Look for both readings when choosing a plug-in meter or an energy-monitoring smart plug.
Read the meter and appliance instructions before connecting them. Check voltage, current and permitted load types; a plug that fits is not proof of compatibility. This guide covers compatible plug-in devices. Leave hardwired equipment and electrical-panel measurements to a qualified professional.
The appliance label is useful for an initial estimate, but actual power can change with settings and operating mode. A laptop charging its battery may give a different reading from the same laptop sitting idle.
Record a normal day, then repeat
Reset the energy total and note the start time. Use the appliance normally, then record the ending kWh and elapsed time. Our suggested starting point is a full day; repeat on different days if your routine varies. This is a practical sampling plan, not a guarantee of annual accuracy.
A device that cycles on and off needs more than a quick glance at its current watts. Refrigerators are one example, but only measure one with equipment explicitly suitable for that appliance. Keep cooling and other essential functions running normally.
- Write down the device, settings, start time, end time and total kWh.
- Mark unusual events, such as a long gaming session or a full battery charge.
- Compare similar days before deciding that a setting changed consumption.
Convert the reading into dollars
Multiply measured kWh by your applicable electricity price in dollars per kWh. For example, a hypothetical reading of 0.8 kWh at an example rate of $0.20/kWh costs $0.16 in energy charges. Replace both inputs with your own numbers.
For a steady load, watts × hours ÷ 1,000 gives kWh. Our calculator uses this approach. It cannot capture cycling automatically, and its monthly and yearly figures assume the same daily use continues.
Use the energy rate from your bill, not a guessed national average. Time-of-use prices need separate calculations for each price period. Fixed charges remain outside this estimate. Pick one sensible change, measure again under similar conditions, and keep the result rather than assuming a saving.
Use your measured power and daily hours in the electricity cost calculator.