Electricity Cost Calculator
Enter device watts, hours per day and your rate to get daily, monthly and yearly energy and cost — the standard appliance running-cost calculation.
Last updated: 2026-09-15
How the calculation works
- Energy = watts × hours ÷ 1000 gives kilowatt-hours; the tool extrapolates to month (30.44 days) and year (365 days).
- Cost multiplies energy by your rate — use the all-in rate including delivery charges for real accuracy.
- The quantity field multiplies the whole calculation for fleets of identical devices (lights, servers, pumps).
Formula
kWh = W × hours ÷ 1000 Cost = kWh × rate
| Symbol | Meaning | Unit |
|---|---|---|
kWh | Energy consumed | kilowatt-hour |
W | Power draw | W |
rate | Price per kWh | $/kWh |
Worked example
A 1500 W space heater running 4 h/day at $0.15/kWh: 6 kWh/day = 182 kWh/month = $27.40/month = $328/year. That number usually convinces people to lower the thermostat.
Interpreting the result
The yearly figure is the one to compare against alternatives: a $400 heat-pump replacement of that heater saving 60% pays back in about 2 years. Devices that run 24/7 (fridges, servers, aquariums) dominate household consumption even at modest wattage.
Assumptions
- Constant wattage while running — devices with compressors cycle and use less.
- Flat electricity rate; tiered or time-of-use pricing needs an average.
Limitations
- Standby consumption (0.5–5 W when 'off') is not counted — add it for always-on electronics.
- Does not model demand charges or fixed connection fees.
Frequently asked questions
How do I find my electricity rate?
Divide the total amount of a bill by the kWh consumed — that all-in figure includes delivery and taxes, which is what you actually pay.
How much does leaving a light on cost?
A 60 W incandescent on 24/7 at $0.15/kWh costs $79/year. An equivalent 9 W LED costs $12/year — the classic efficiency argument.