Energy Cost Calculator — Electricity Cost of Any Device
Electrical & EnergyHow much does it cost to run? Enter the wattage, how long it runs and your rate per kWh to get the cost per hour, month and year.
Rates and tables verified: · sources
Last updated: October 2026
Utilities bill electricity by the kilowatt-hour (kWh): 1,000 watts running for one hour. Multiply a device's wattage by its hours of use, divide by 1,000, and you have the kWh. Multiply by your rate and you have the cost. This energy cost calculator does that for one device or several identical ones. It accounts for days of use per week, so a work computer used five days a week isn't billed like a fridge running every day. It reports cost per hour of use, the average per day, and totals per month and year. The rate box starts at the US residential average from the Energy Information Administration (17.99¢/kWh, 12 months ending July 2026). Rates vary widely by state and utility, so replace it with yours. Dividing your bill's total by the kWh it lists gives an all-in rate that includes delivery charges.
How to Calculate Electricity Cost
1. Find the device's power draw in watts. It is on the label or charger, or you can measure it with a plug-in energy meter for devices whose draw varies. 2. kWh per day of use = watts × hours per day × number of devices ÷ 1,000. 3. Yearly kWh = kWh per day of use × days per week × 52.14 (365 ÷ 7). 4. Monthly kWh = yearly ÷ 12. 5. Cost = kWh × your rate per kWh.
Formula
kWh per use-day = W × h × qty ÷ 1000 kWh per year = kWh per use-day × days/week × 365 ÷ 7 kWh per month = kWh per year ÷ 12 Cost = kWh × rate ($/kWh) Cost per hour = W × qty ÷ 1000 × rate W — power draw in watts h — hours used per day qty — number of identical devices rate — price per kWh
Electricity Cost Examples
Example 1 — 1,500 W space heater, 4 h/day, at 17.99¢/kWh
1,500 × 4 ÷ 1000 = 6 kWh per day Per month: 182.5 kWh × $0.1799 = $32.83 Per year: 2190 kWh × $0.1799 = $393.98
Example 2 — 10 W device left on 24/7, at 17.99¢/kWh
10 × 24 ÷ 1000 = 0.24 kWh per day Per year: 87.6 kWh → $15.76
Example 3 — Four 150 W office PCs, 8 h/day, 5 days/week, at 13¢/kWh
150 × 8 × 4 ÷ 1000 = 4.8 kWh per workday Per year: 4.8 × 5 × 52.14 = 1251 kWh → $162.69 Per month: $13.56
Tips for an Accurate Estimate
- › Label wattage is often a maximum. Fridges, AC units and PCs cycle or vary their draw, so a plug-in meter reading over a day gives a truer kWh.
- › Use your all-in rate (total bill ÷ kWh) rather than the headline energy charge, which leaves out delivery and other per-kWh fees.
- › Time-of-use plans charge different rates at different hours. Run the calculation once per rate period if a device runs across them.
- › Planning a new circuit for a big load? Convert its watts with the amp calculator, then size the wire with the wire size calculator.
Assumptions, Sources & Limitations
What this calculator assumes
- Constant power draw while the device is in use. For cycling appliances, enter an average wattage or measured kWh-equivalent hours.
- A year is 365 days and a month is one-twelfth of a year. "Cost per day" is the yearly cost averaged over every day, including days the device is off.
- The default rate is the US residential average, 17.99¢/kWh, for the 12 months ending July 2026. EIA Electric Power Monthly (released 2026-09-24), Table 5.3, rolling 12-month average. Preliminary. Latest single month (July 2026): 18.31¢/kWh; full-year 2025: 17.30¢/kWh. Your own rate varies by state, utility, plan and time of use.
- Tiered and time-of-use pricing, fixed monthly charges and taxes are not modeled. Enter an all-in rate to include them approximately.