Electricity Cost Calculator
Estimate appliance electricity use and cost from power, runtime, schedule, device count, and price per kWh.
Content updated August 4, 2026
Nameplate power multiplied by scheduled runtime is an estimate. Cycling loads, standby use, efficiency, and actual metered tariffs can change the bill.
Estimate how much electricity one appliance or a group of identical devices uses from rated power and scheduled runtime. Enter watts or kilowatts, number of devices, hours on each active day, active days per week, and the energy price from your bill.
The result separates energy in kilowatt-hours from money. It shows an active-day estimate, weekly totals, annualized average monthly totals, and yearly totals without assuming a country, utility, currency, or tariff.
The Electricity Cost formula
Energy per active day (kWh) = power (W) ÷ 1,000 × devices × hours · Cost = energy (kWh) × price per kWhWeekly energy multiplies by active days/week · annual energy = weekly energy × 365.2425 ÷ 7 · average monthly energy = annual energy ÷ 12.
Worked example
One 1,500 W appliance used two hours every day consumes 1.5 × 2 = 3 kWh per day and 21 kWh per week. At 0.15 per kWh, that is 0.45 per active day, 3.15 per week, and about 164.36 per annualized year.
Assumptions, rounding, and limitations
Assumptions
- Each device draws the entered rated power continuously during every entered runtime hour.
- All devices are identical and follow the same weekly schedule.
- The entered price is one flat energy charge per kWh in the selected currency.
- A year is 365.2425 days for annualizing the repeating weekly schedule; an average month is one twelfth of that year.
Rounding: Energy and cost calculations retain floating-point precision. Energy displays show up to three decimals and money displays round to two currency decimals.
Limitations
- Does not model cycling, variable load, power factor, startup current, battery losses, standby consumption outside the entered schedule, or measured usage uncertainty.
- Does not include fixed charges, taxes, tariff tiers, time-of-use prices, demand charges, minimum bills, adjustments, credits, or exchange rates.
- The result is an estimate from rated power and schedule, not a utility meter reading or electrical-safety assessment.
Sources
- Measuring Electricity — U.S. Energy Information Administration
- Kilowatthour Definition — U.S. Energy Information Administration
From power to energy
The U.S. Energy Information Administration explains that watts measure power at a moment, while watt-hours measure energy used over time. One kilowatt is 1,000 watts, and one kilowatt-hour is one kilowatt sustained for one hour.
This calculator divides watts by 1,000, multiplies by device count and runtime, then applies active days. Annual use scales the weekly schedule by 365.2425 ÷ 7; the average month is that annual result divided by 12.
Why a bill can differ from the estimate
A nameplate rating may be maximum input rather than average draw. Refrigerators, air conditioners, heaters, chargers, and other cycling or variable-power equipment can spend only part of the schedule at full rated power, while standby use may continue outside it.
The entered price per kWh is applied as one flat energy charge. Real tariffs can include fixed customer charges, taxes, time-of-use rates, tiers, demand charges, fuel adjustments, minimum bills, net-metering credits, and other rules.
Frequently asked questions
▶How do I convert watts and hours to kWh?
Multiply watts by hours and divide by 1,000. A 1,500-watt appliance running for two hours uses 3 kWh.
▶How is electricity cost calculated?
Multiply energy in kWh by your entered price per kWh. Use the energy charge from your bill in the selected currency.
▶Why is the monthly result called an average?
The weekly schedule is annualized across 365.2425 days and divided by 12. Actual calendar months have different lengths and may have different schedules.
▶Can I calculate several identical appliances?
Yes. Enter a whole-number device count; power and energy scale by that number.
▶Will this match my utility bill exactly?
Not necessarily. Actual metered power, cycling, standby use, schedule changes, tariff tiers, taxes, fixed charges, demand charges, and credits can change the bill.
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Open calculator →Disclaimer: Electricity Cost Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.