What this calculator tells you
The calculation assumes the appliance draws the entered wattage for all entered hours. Devices that cycle on and off or change power dynamically may use less or more than a simple nameplate estimate suggests.
Formula
Worked example
Useful for
- Estimating the running cost of a heater, appliance or electronic device
- Comparing devices with different power ratings
- Checking whether reducing runtime could materially affect energy use
Common mistakes
- Confusing watts with kilowatts. The calculator converts watts to kilowatts for you.
- Assuming a device draws its maximum rated wattage continuously.
- Ignoring standby use or multiple devices when estimating a whole-room total.
How to get a more useful estimate
Use inputs that match the decision you are actually making. If a price, rate, efficiency or usage figure can vary, run the calculator more than once with a low, expected and high case. Keep units consistent, avoid rounding intermediate values too early, and separate costs that this calculator does not include.
Frequently asked questions
How do I convert watts to kW?
Divide watts by 1,000. A 1,000-watt device is 1 kW.
Does a 1,000-watt appliance always use 1 kWh every hour?
Only if it actually draws 1,000 watts continuously for the full hour.
Can I estimate monthly cost?
Yes. Enter the total number of hours you expect the appliance to run during the month.
Related tools and guides
This calculator is a planning tool. For contracts, taxes, regulated charges, loans or other decisions with legal or financial consequences, verify the final figures and terms with the relevant provider or authority.