1. Use the right electricity rate
Enter a price per kWh from a recent bill. If your bill has tiered or time-of-use prices, use the rate that applies when the appliance runs, or calculate an effective rate by dividing relevant electricity charges by billed kWh. Fixed monthly fees usually do not change when one appliance uses less electricity.
2. Choose the best power source
| Input source | Best use | Main limitation |
|---|---|---|
| Measured kWh | Cycling or variable loads measured over representative time | A short or unusual sample can mislead |
| Measured watts | Stable loads at the operating mode you care about | A snapshot can miss cycles and modes |
| Device label | Upper-bound or rough planning | Nameplate power is not always typical power |
| Illustrative preset | Fast comparison when no product data is available | Real models and behavior vary widely |
3. Measure long enough
For a television or heater at a stable setting, a shorter reading may be useful. Refrigerators, washers, game consoles, and sleep/standby devices change modes: measure complete cycles and representative behavior. A refrigerator measurement is more representative when it spans at least a full day, and longer when room temperature or defrost cycles vary.
4. Avoid double-counting standby
If your kWh measurement includes both active and idle time, treat it as the whole measured period and do not add the same standby energy again. In the calculator, separately entered standby applies only outside scheduled active time.
5. Interpret small differences cautiously
Two options that differ by only a few currency units per year may be effectively tied once behavior, rates, and measurement uncertainty are considered. Safety, performance, durability, and purchase price can outweigh a small energy estimate.
For formula details, see the methodology. For source provenance, see data sources.
Last reviewed: August 14, 2026