A quick way to turn watts and hours into kilowatt-hours and a dollar cost. Enter the power in watts, the number of hours, and the rate you pay per kWh — the tool returns the energy used and what it costs. The preset (1,000 W for 5 hours at $0.15/kWh) uses 5 kWh and costs $0.75. It is the plain kWh-cost math behind every appliance, charger or tool you run.
Results are estimates for planning and education, based on your inputs and standard engineering values (AWG resistance, NEC ampacity, resistivity). Electrical work can be dangerous and is governed by the NEC and your local code — verify all sizing with a licensed electrician and your authority having jurisdiction (AHJ). Not a substitute for professional design.
Calculator
Energy used
5.00 kWh
Cost
0.75 $
Formula
Kilowatt-hours = watts × hours ÷ 1,000. Cost = kWh × your rate ($/kWh). A kilowatt-hour is the energy of one kilowatt drawn for one hour, the unit your utility bills you in. Divide watts by 1,000 to get kilowatts, multiply by the hours of use for kWh, then multiply by the price you pay. No rate is stored here — you enter your own, so the answer stays current.
Worked example
A 1,000-watt microwave or heater runs for 5 hours. Energy = 1,000 × 5 ÷ 1,000 = 5 kWh. At $0.15 per kWh the cost is 5 × 0.15 = $0.75. Double the power to 2,000 watts and the energy doubles to 10 kWh and the cost to $1.50; halve the hours and both halve. Energy and cost both scale straight in line with watts, hours and rate.
Kilowatt-hours are how the utility bills you, and this calculator turns an energy figure straight into money at the rate you enter. It is the companion to a meter reading or an estimate from the watt-hours tool: once you know the energy a task consumes, multiplying by your rate gives its cost, and dividing a monthly bill by its kilowatt-hours tells you the rate to plug back in elsewhere. Keeping the rate as your own input keeps the tool honest and maintenance-free across regions and over time. Bear in mind that a single per-kWh figure cannot capture time-of-use pricing, tiered rates or fixed standing charges, so for a precise bill compare against the tariff on your own statement.
Frequently asked questions
What is a kilowatt-hour (kWh)?
A kilowatt-hour is the amount of energy used by a one-kilowatt (1,000-watt) load running for one hour. It is the unit utilities bill you in. A 100-watt bulb left on for 10 hours uses 1 kWh; a 2,000-watt heater uses 1 kWh in just half an hour. Because it combines power and time, the kWh is the right unit for comparing the running cost of very different devices on the same footing.
How do I convert watts to kilowatt-hours?
Multiply the watts by the hours of use, then divide by 1,000: kWh = watts × hours ÷ 1,000. For instance 1,500 watts for 2 hours is 1,500 × 2 ÷ 1,000 = 3 kWh. If you already know the power in kilowatts, just multiply kilowatts by hours and skip the division. Watts measure the rate of use; kWh measure the total energy consumed over time.
How do I work out the cost per kWh?
Divide the total dollar amount of your electricity bill by the kilowatt-hours you used in that period. This blended rate already includes supply, delivery, taxes and fixed-fee allocation, so it reflects what each extra kWh truly costs you. Using this figure rather than just the listed energy charge gives a more honest running cost, since delivery and fees can be a large share of the bill.
How is this different from the appliance cost calculator?
They use the same core math. This kWh-cost tool is the general helper: enter any wattage, a number of hours and a rate to get the energy and cost of that single run. The appliance cost calculator takes hours per day and projects the figure out to a daily, monthly and yearly total. Use this one for a quick one-off run, and the appliance tool when you want ongoing cost over time.
Does power factor affect the cost for home appliances?
For residential customers, generally no. Home meters bill real energy in kWh, and the watt figure on a nameplate already reflects real power, so volts × amps × hours overstates it slightly for motors but kWh billing ignores the difference. Power factor mainly matters to commercial and industrial accounts that face demand or reactive-power charges. For a house, multiplying real watts by hours and your rate is accurate enough.
Why does the calculator not include a fixed electricity price?
Because electricity rates differ by state, utility, plan and time of year, and they change over time. Hardcoding a price would make the answer wrong for most users and stale within months. Entering your own rate from your bill keeps the calculation correct for your situation and means the tool never needs updating. The math (watts × hours ÷ 1,000 × rate) is timeless; only the rate is local to you.
Source: kWh = watts × hours ÷ 1,000; cost = kWh × the user-entered $/kWh rate (no tariff hardcoded). · All sources