Electricity Calculator
Work out an appliance's electricity use and what it costs per day, month and year.
About Electricity Calculator
Energy use is calculated as watts × hours ÷ 1000 to get kilowatt-hours (kWh). An optional standby power adds a small continuous load for the hours the device is plugged in but idle. The daily kWh figure is then scaled to monthly (× 30.44) and yearly (× 365.25). Cost is simply kWh × the utility rate. The CO₂ equivalent uses the US EPA 2023 national average grid emission factor of 0.386 kg CO₂e per kWh.
Formulas
Daily kWh
Daily kWh = (watts × hours + standby_watts × (24 − hours)) ÷ 1000
- P
- Active power (W)
- t
- Hours used per day
- P_{sb}
- Standby power (W)
Cost
Annual cost = annual kWh × rate per kWh
Worked example
With the default values below, Electricity Calculator returns Monthly Cost of $7.31. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Appliance Powerminimum 0.1 W
- 1,500 W
- Hours Used per Dayaccepts 0–24 h/day
- 1 h/day
- Standby Poweraccepts 0–50 W
- 0 W
- Electricity Rateminimum 0.001 $/kWh
- 0.16 $/kWh
- Days per Monthaccepts 1–31 days
- 30.44 days
Results
- Monthly Cost
- $7.31
- Annual Cost
- $87.66
- Daily Cost
- $0.2400
- Daily Use
- 1.5000 kWh
- Monthly Use
- 45.660 kWh
- Annual Use
- 547.88 kWh
- CO₂ EquivalentBased on US average grid emission factor of 0.386 kg CO₂/kWh.
- 211.5 kg/year
Step by step
- 1Active energy (daily)= 1.5000 kWh/day
- 2Total daily use= 1.5000 kWh/day
- 3Monthly use= 45.660 kWh/month
- 4Monthly cost= $7.31/month
- 5Yearly cost= $87.66/year
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Where do I find my appliance's wattage?
Check the label on the back or bottom of the appliance, or the user manual. It may be listed as 'Rated Power' or 'Maximum Power'. If listed in amps and volts, multiply them: W = A × V.
What is the average US electricity rate?
As of 2024, the US residential average is approximately $0.16/kWh (EIA). Rates vary significantly by state — California averages ~$0.25/kWh, while Louisiana averages ~$0.10/kWh.
What is standby power?
Many appliances draw power even when not in use — TVs with remote receivers, microwaves with clocks, phone chargers, game consoles. This 'vampire' draw is typically 0.5–5 W per device but adds up across a household.
How do I lower my electricity bill?
Target the highest-wattage appliances used most often. Electric water heaters, HVAC systems and electric dryers typically dominate. Switching to LED lighting and unplugging standby devices saves a smaller but still meaningful amount.