To calculate electricity cost: Watts ÷ 1,000 × Hours Used × Cost per kWh = Cost. A 100-watt bulb running 8 hours at $0.15/kWh costs $0.12/day ($3.60/month). A 1,500-watt space heater running 4 hours daily costs $0.90/day ($27/month).
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What Is an Electricity Cost Calculator?
An electricity cost calculator is a tool that determines how much it costs to run any electrical appliance or device, based on its power consumption (in watts), how long it runs, and your local electricity rate (in cents per kilowatt-hour, or kWh).
Electricity is billed in kilowatt-hours. One kilowatt-hour equals 1,000 watts running for one hour. Your utility bill shows your total monthly kWh usage multiplied by your rate. The US national average electricity rate is approximately $0.14–$0.16 per kWh, but rates vary significantly by state: Louisiana averages around $0.09/kWh while Hawaii exceeds $0.40/kWh.
Knowing the cost to run individual appliances helps you identify your biggest electricity consumers and prioritize efficiency improvements. Heating and cooling equipment (central AC, electric heaters, water heaters) typically dominate home electricity use. The difference between an efficient and an inefficient appliance can translate to hundreds of dollars per year.
An electricity cost calculator takes the wattage of any device (found on its label, power supply, or manufacturer specs), the daily hours of use, and your kWh rate, then outputs daily, monthly, and annual operating costs. This makes it easy to compare appliances before buying, justify efficiency upgrades, or evaluate whether a behavior change (like running the dishwasher less often) is worth the effort.
The Electricity Cost Formula
kWh = Watts × Hours ÷ 1,000
Cost = kWh × Price per kWh
Find your electricity rate on your utility bill (US average: $0.12–$0.18 per kWh; national average in 2024: ~$0.14/kWh). Some states are significantly higher (California: ~$0.25/kWh; Hawaii: ~$0.40/kWh) or lower (Louisiana: ~$0.09/kWh).
Appliance Wattage Reference
| Appliance | Typical Wattage | Daily Use | Monthly Cost @ $0.15 | |-----------|---------------|-----------|---------------------| | LED bulb | 10W | 5 hrs | $0.23 | | Incandescent bulb | 60W | 5 hrs | $1.35 | | LED TV (55") | 80W | 5 hrs | $1.80 | | Refrigerator | 150W | 24 hrs | $16.20 | | Window AC unit | 1,200W | 8 hrs | $43.20 | | Central AC | 3,500W | 8 hrs | $126.00 | | Electric dryer | 5,000W | 1 hr | $22.50 | | Dishwasher | 1,200W | 1 hr | $5.40 | | Microwave | 1,100W | 0.5 hr | $2.48 | | Desktop computer | 200W | 8 hrs | $72.00 | | Laptop | 50W | 8 hrs | $18.00 | | Phone charger | 5W | 8 hrs | $1.80 | | Space heater | 1,500W | 4 hrs | $27.00 | | Water heater (electric) | 4,000W | 3 hrs | $54.00 |
LED vs. Incandescent Savings
Replacing one 60W incandescent with a 10W LED (same light output):
- Daily savings: (60−10)W × 5hrs ÷ 1,000 × $0.15 = $0.0375/day
- Annual savings: $13.69/bulb/year
- For 20 bulbs: $274/year in electricity savings
- LED bulb costs more upfront (~$5 vs. $1 for incandescent), but pays back within 1–2 months
Phantom Load (Standby Power)
Many devices draw power even when "off" or in standby mode:
| Device | Standby Wattage | Monthly Cost | |--------|----------------|-------------| | Cable box | 15–30W | $1.62–$3.24 | | Game console | 0.5–11W | $0.05–$1.19 | | TV (standby) | 0.5–2W | $0.05–$0.22 | | Microwave (clock) | 3W | $0.32 | | Laptop charger (plugged in) | 1–5W | $0.11–$0.54 | | Average US home (all phantom) | ~100W constant | $10.80/month |
Smart power strips and smart plugs eliminate phantom load for devices that don't need to be on 24/7.
Frequently Asked Questions
How do I find the wattage of my appliances? Look for a label on the appliance itself (usually on the back or bottom). The label shows watts (W) or amps (A) and volts (V). If you see amps and volts but not watts: Watts = Amps × Volts. A device drawing 8.5 amps at 120V: 8.5 × 120 = 1,020 watts. For more accurate measurement of actual consumption (which varies by load), use a plug-in watt meter (Kill A Watt, $25–30) that measures real-time wattage, kWh consumed, and cost.
How is kWh calculated on my electric bill? Your utility meter records total kilowatt-hours consumed. kWh = watts × hours ÷ 1,000. Your bill shows: kWh used × rate per kWh = base charge, plus fixed fees (meter charge, distribution, taxes). Some utilities have tiered pricing — the first 500 kWh/month might be $0.10/kWh; the next 500 kWh might be $0.15/kWh; above 1,000 kWh might be $0.20/kWh. Time-of-use (TOU) plans charge more during peak hours (afternoons) and less at off-peak times (nights, weekends).
Which appliances cost the most to run? The highest electricity consumers in a typical home: (1) HVAC (heating/cooling) — 40–50% of total electricity; (2) Water heater — 14–18%; (3) Refrigerator — 13–14%; (4) Washer and dryer — 5–8%; (5) Lighting — 5–8%; (6) Dishwasher — 3%. Reducing HVAC usage through better insulation, thermostat setbacks, or efficiency upgrades has the highest return. After HVAC, the refrigerator and water heater are the next highest targets for savings.
How much can I save by using a smart thermostat? The US Department of Energy estimates that setting your thermostat back 7–10°F for 8 hours per day (while sleeping or away) saves 10% per year on heating and cooling costs. For a household spending $200/month on HVAC (typical for a mid-size home), that's ~$240/year savings. Smart thermostats (Nest, Ecobee) also learn patterns and automate setbacks. They pay for themselves in 1–2 years for most households.
What is the difference between watts and kilowatts? 1 kilowatt (kW) = 1,000 watts (W). Watts measure power (rate of energy use at a moment in time). Kilowatt-hours (kWh) measure energy (power used over time): 1 kW × 1 hour = 1 kWh. A 1,000-watt (1 kW) device running for 1 hour consumes 1 kWh of electricity. A 100-watt device running for 10 hours also consumes 1 kWh. Your electric bill charges you per kWh, not per watt.
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Calculate Your Electricity Cost Now
The free Electricity Cost Calculator at RoughTools calculates daily, monthly, and annual electricity costs for any appliance by wattage and usage hours. Add multiple appliances to estimate total home electricity cost. No account needed, completely free.