Kill A Watt Electricity Cost Calculator
Estimate daily, monthly, and yearly electricity use and cost from measured kWh and an observation period.
Measured Energy Estimate
- Cost per day
- Cost per year
- Measured-period cost
- Average energy per day
- Estimated energy per 30-day month
- Estimated energy per 365-day year
- Average watts during measurement
This measurement is shorter than 24 hours. Make sure it represents normal use. For cycling equipment, measure multiple complete cycles and preferably several typical days when practical.
Month = 30 days. Year = 365 days. Projections assume the measured average continues.
How it works
Divide accumulated kWh by the observation hours to find average energy use per hour.
kWh/month = kWh/day × 30
kWh/year = kWh/day × 365
Cost = kWh × (cents per kWh ÷ 100)
Average watts = measured kWh × 1,000 ÷ observation hours
Example: 1.2 kWh over 24 hours at 16¢/kWh gives 36 kWh and $5.76 per 30-day month, or 438 kWh and $70.08 per 365-day year.
Assumptions and useful information
A Kill A Watt or similar meter measures energy over time. Use the accumulated kWh reading and its matching elapsed period. This differs from estimating use from an appliance wattage rating.
Choose representative operation, including idle time. For refrigerators, freezers, dehumidifiers, sump pumps, and other cycling equipment, measure multiple complete cycles and preferably several typical days when practical. A steady load may be represented by a shorter observation, but forecasts still depend on typical usage.
Average watts includes observed idle and cycling behavior. It is not necessarily running wattage or startup wattage. No extra duty-cycle correction is applied.
Seasonal conditions and operating habits may change future consumption. A zero meter reading does not prove zero consumption. The rate is constant; fixed charges and fees not included in that rate are excluded.