Updated September 13, 2026 · WattCostLab Calculator
Electricity Cost Calculator
Reviewed by WattCostLab Editorial Team · Methodology and source assumptions are documented below.
Calculate the running cost of any appliance or device. Start with a preset, choose a state reference rate, then replace the examples with your actual wattage, runtime and utility tariff.
Calculate electricity cost
Presets are practical starting values, not model-specific ratings. Replace them with measured or manufacturer data when available.
State values are 2024 final EIA averages; the U.S. reference is 2025. Your actual tariff can differ.
Cost by daily usage
Same wattage and electricity rate; only daily runtime changes.
| Usage | kWh/month | Monthly cost | Annual cost |
|---|
How this calculator works
The calculator converts power and runtime into energy before applying your electricity price. The daily energy formula is watts × hours per day ÷ 1,000 = kWh/day. Daily cost is then kWh/day × your entered electricity rate. WattCostLab multiplies that daily cost by 30.4375 for the monthly estimate and by 365 for the annual estimate. Those multipliers keep the arithmetic transparent: the tool does not add taxes, fixed customer charges or demand charges that are not represented in your per-kWh input.
The appliance presets are starting points only. A device labeled 1,500 W does not necessarily draw exactly 1,500 W every minute it is operating. Thermostatically controlled equipment, variable-speed motors and electronics can cycle or change power during use, so measured average power is better than a nameplate maximum when you have it.
Worked example: a 1,500 W heater used for one hour
Using the page defaults — 1,500 W, 1 hour/day and $0.173/kWh — the calculator performs the following steps:
- Daily energy: 1,500 × 1 ÷ 1,000 = 1.50 kWh/day.
- Daily cost: 1.50 × $0.173 = $0.26/day.
- Monthly estimate: $0.2595 × 30.4375 = about $7.90/month.
- Annual estimate: $0.2595 × 365 = about $94.72/year.
If the same heater runs for four hours instead of one, energy and cost are roughly four times higher because runtime enters the formula linearly. If your utility rate is twice the reference rate, the energy use stays the same but the cost doubles.
Why your utility bill can differ
This is an appliance-energy calculation, not a bill replica. Utilities may use time-of-use periods, tiered rates, seasonal prices, fixed customer charges, minimum bills, taxes or other adjustments. The U.S. Energy Information Administration also distinguishes an average retail electricity price from an individual utility tariff: an average price is derived from revenue divided by sales and is not necessarily the rate applied to your specific account. For the closest estimate, use the effective energy rate from your own bill or the rate for the hours in which the device actually runs.
For cycling appliances such as refrigerators, heat pumps and air conditioners, use measured kWh from a smart plug, submeter or utility interval data when possible. If you only know rated watts, treat the result as a planning estimate rather than a measurement.
When this estimate is most useful
Use this calculator to compare devices, test schedule changes, estimate the cost of a new load or understand how much a particular appliance contributes to household consumption. For whole-home billing, compare the result with your utility statement and include charges that are not expressed per kWh. For official U.S. reference data, see the U.S. EIA electricity sales, revenue and average-price data.
How to find your electricity rate
Look for the energy charge on your utility bill and convert cents per kWh to dollars per kWh. A rate of 17.3¢/kWh equals $0.173/kWh. Fixed customer charges, time-of-use pricing and taxes can make the total bill differ from a simple energy-only calculation.
How to find watts or kWh
Use measured power, manufacturer data or an EnergyGuide/annual kWh value. If a device cycles, measure over a representative period instead of assuming it draws maximum power continuously.
Popular appliance calculations
Air conditioner cost · dryer cost · oven cost · dehumidifier cost · refrigerator cost.
Estimates only. Actual bills can include fixed charges, taxes, tiers, time-of-use pricing or demand-related components.
WATTCOSTLAB / COST PLANNING
How to calculate electricity cost from watts and hours
Divide watts by 1,000 to convert power to kilowatts, multiply by operating hours to get kWh, then multiply by the electricity price per kWh. The same method works for appliances, heaters, pumps, EV charging and other electrical loads.
Cost per hour, day, month and 100 kWh
Use the actual effective electricity rate from your bill whenever possible. State or national averages are useful reference values, but they can differ from your utility tariff, supplier plan, taxes and time-of-use pricing.
Related calculators and guides
Quick questions
How much does 100 watts cost per hour?
A 100-watt load uses 0.1 kWh in one hour. Multiply 0.1 kWh by your electricity rate to calculate the cost for that hour.
How do I convert watts to monthly electricity cost?
Convert watts to kW, multiply by hours used per day and days per month, then multiply the resulting kWh by your electricity price.
WATTCOSTLAB / EXTERNAL EXPLAINER
Watch: How time-of-use electricity rate plans work
Time-of-use plans charge different electricity prices at different times of day. This explainer provides context for why the same appliance can cost more or less to run depending on when energy is used.
External educational video by Southern California Edison (SCE). The video explains the concept; use the WattCostLab tools and inputs on this page for your own rates, location and assumptions. Watch on YouTube.
Make this estimate closer to your real bill
Reviewed September 14, 2026. For a device that cycles, measured kWh is usually more useful than maximum nameplate watts. For a time-of-use tariff, run separate scenarios for peak and off-peak periods instead of applying one blended rate to every hour.
Example sensitivity. A 1.5 kW load used 2 h/day consumes 91.3 kWh in an average month. At $0.15/kWh the energy portion is about $13.69/month; at $0.30/kWh it is about $27.39/month. The calculator intentionally keeps the tariff editable so the assumption is visible.
EIA Electric Power Monthly → · Compare state reference prices →