Energy planning / BROWSER TOOL
Electricity Cost Calculator
Estimate electricity use and running costs for a single appliance or a group of devices. Enter the power, daily operating hours and your own price per kWh to compare daily, monthly and yearly costs.
ESTIMATED MONTHLY ENERGY COST
30-day month · 365-day year · USD 0.30/kWh
- Daily electricity use
- 2.4 kWh
- Monthly electricity use
- 72 kWh
- Yearly electricity use
- 876 kWh
- Daily cost
- USD 0.72
- Yearly cost
- USD 262.80
Cost by device
| Device | kWh/day | Cost/month |
|---|---|---|
| Example device × 1 | 2.4 | USD 21.60 |
Energy charges only, using a flat rate and the same daily usage throughout the period. Fixed fees, taxes, demand charges, tiered rates and time-of-use pricing are excluded. Costs are rounded to two decimals; positive costs below 0.01 are labelled.
How to use the electricity cost calculator
Find the energy price on your electricity tariff or bill, expressed in currency per kilowatt-hour. If it is listed as 30 cents per kWh, enter 0.30 rather than 30. Enter the device's average power while operating and its hours of use each day. Use quantity for identical devices with the same schedule, or add a separate row when their power or hours differ.
Select a month length from 1 to 31 days. The annual estimate always uses 365 days, so it does not equal twelve 30-day months. Currency selection controls the displayed currency code only. Enter your tariff in that currency; no exchange rate or regional electricity price is fetched.
Electricity cost formula: watts to kWh to cost
Daily energy (kWh) = power (W) × hours per day × quantity ÷ 1,000. Multiply daily kWh by the selected number of days for the monthly energy estimate, or by 365 for the yearly estimate. Energy cost equals kWh multiplied by your price per kWh. With power entered in kW, the conversion from watts is unnecessary.
Worked example: a 100-watt device running all day
A device drawing 100 W for 24 hours uses 2.4 kWh per day. At the illustrative rate of USD 0.30/kWh, that is USD 0.72 per day, USD 21.60 for 30 days and USD 262.80 for 365 days. Its yearly consumption is 876 kWh. These are calculations from the example inputs, not a claim about a particular appliance or local tariff.
Choosing realistic power and operating hours
A rated maximum is not always the average draw. Refrigerators, heaters and air conditioners can cycle, while PCs and servers change consumption with workload. Either enter an average power measured over the operating period, or use separate rows for active and idle periods. For one device, those periods should add up to no more than 24 hours per day. Do not count the same consumption twice.
If an energy meter reports kWh over several days, divide by the number of measured days to estimate daily energy. To model that as a constant 24-hour load here, multiply daily kWh by 1,000 and divide by 24 to obtain average watts. That measurement already includes the device's active, idle and standby behavior during the sample.
Frequently asked questions
What is the difference between kW and kWh?
Kilowatts describe power at a moment in time. Kilowatt-hours describe energy accumulated over time. A constant 1 kW load operating for two hours consumes 2 kWh. Your energy tariff is normally expressed per kWh, rather than per kW.
Can I calculate the cost of running a server or NAS 24/7?
Yes. Enter its average measured power at the wall and 24 hours per day. A power supply's 500 W rating describes its capacity, not proof that the server draws 500 W. Include switches, storage devices or a UPS as separate loads only when their energy is not already included in the measurement.
Can I add several appliances together?
Yes. Add up to 32 device rows with individual power and operating hours. Quantity multiplies a row's energy use, and the results include a cost breakdown. Different operating modes of one appliance may also use separate rows, provided their hours do not overlap.
Does this predict my entire electricity bill?
No. It estimates the energy charge for the loads you enter at one flat rate. Your bill may also include standing charges, taxes, discounts, different price tiers or rates that change by hour. With time-of-use pricing, calculate each rate period separately using its applicable hours and price, then add those energy charges.
Why does my real consumption differ from this estimate?
The model repeats the entered power and daily schedule for every day. Real workloads, thermostat cycles, seasonal use and standby draw can change. Use measured average power and representative hours, then compare the calculated kWh with your meter over the same period.
Plan the rest of your setup
Estimate usable disk capacity with the RAID / ZFS calculator, or plan a backup window with the download and upload time calculator. For an always-on lab, the Proxmox backup guide explains the backup and restore workflow.
Reference and calculation method
The U.S. Department of Energy's energy-use education material (PDF) explains energy and cost calculations from appliance power, operating hours and an electricity rate. This calculator uses that unit conversion and your inputs. It does not import the document's example appliance ratings or prices.