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US average: $0.12/kWh. Check your electricity bill for actual rate.
kWh = Watts × Hours ÷ 1000
Where:
| Appliance | Watts | Hours/Day | Monthly kWh |
|---|---|---|---|
| LED Light Bulb | 10W | 5h | 1.5 kWh |
| Laptop | 50W | 8h | 12 kWh |
| Desktop Computer | 200W | 8h | 48 kWh |
| Television (50") | 100W | 4h | 12 kWh |
| Refrigerator | 150W | 24h | 108 kWh |
| Air Conditioner | 1500W | 8h | 360 kWh |
| Space Heater | 1500W | 6h | 270 kWh |
| Washing Machine | 500W | 1h | 15 kWh |
| Electric Dryer | 3000W | 1h | 90 kWh |
| Microwave | 1000W | 0.5h | 15 kWh |
| Coffee Maker | 900W | 0.25h | 6.75 kWh |
| Hair Dryer | 1800W | 0.25h | 13.5 kWh |
* Values are estimates. Actual consumption varies by model, settings, and usage patterns.
Watts to kWh conversion transforms an instantaneous power measurement (watts) into a cumulative energy measurement (kilowatt-hours) over a given period. The kilowatt-hour is the standard unit used by electric utilities worldwide to bill customers for electricity consumption. One kWh equals the energy used by a 1000-watt device running for one hour, or equivalently, a 100-watt device running for 10 hours. The formula is straightforward: kWh = Watts × Hours ÷ 1000. This conversion is essential for estimating electricity costs, comparing appliance efficiency using EnergyGuide labels mandated by the FTC, sizing solar panel systems, and tracking energy budgets. The U.S. Energy Information Administration (EIA) reports that the average American household consumes about 886 kWh per month, making this calculation one of the most practical in everyday electrical engineering.
Check the appliance nameplate, EnergyGuide label, or use a plug-in power meter. The wattage may be listed directly or calculated from volts and amps (W = V × A). For variable loads like refrigerators, use the average or estimated annual kWh from the EnergyGuide label.
Determine how many hours per day the device runs. Some run continuously (refrigerators, though they cycle on/off), while others run intermittently (dryers at ~1 hour, microwaves at ~0.5 hours). Be realistic about actual usage patterns.
Apply the formula: kWh = Watts × Hours ÷ 1000. For daily usage, multiply hours per day. For monthly, multiply by 30. For example, a 200W TV watched 4 hours/day for a month: 200 × 4 × 30 ÷ 1000 = 24 kWh/month.
Multiply kWh by your electricity rate (found on your utility bill). Cost = kWh × Rate. For the TV example at $0.16/kWh: 24 × $0.16 = $3.84/month. Check if your utility uses tiered or time-of-use pricing for more accurate estimates.
Understanding kWh consumption lets you identify the most expensive appliances and make informed decisions about usage habits. Replacing a 60W incandescent with a 10W LED saves about 18 kWh per month if used 12 hours daily — about $2.90/month per bulb.
Solar panel systems are sized based on kWh consumption. Knowing your total daily kWh usage lets you calculate the right system size. A home using 30 kWh/day in an area with 5 peak sun hours needs a 6 kW system (30 ÷ 5) before accounting for losses.
Each kWh of grid electricity produces about 0.86 pounds of CO₂ (US average per EPA eGRID). Tracking kWh consumption directly ties to carbon footprint calculations, helping households and businesses meet sustainability goals and comply with energy reporting requirements.
| Appliance | Watts | Hours/Day | kWh/Month | Cost/Month* |
|---|---|---|---|---|
| LED Bulb (60W equiv.) | 10 W | 8 h | 2.4 kWh | $0.38 |
| Laptop Computer | 50 W | 8 h | 12 kWh | $1.92 |
| 50" Television | 100 W | 5 h | 15 kWh | $2.40 |
| Refrigerator | 150 W | 8 h (avg) | 36 kWh | $5.76 |
| Electric Water Heater | 4500 W | 3 h | 405 kWh | $64.80 |
| Central Air Conditioner | 3500 W | 8 h | 840 kWh | $134.40 |
| EV Charger (Level 2) | 7200 W | 4 h | 864 kWh | $138.24 |
* Estimated at $0.16/kWh (US average). Actual rates vary by region and utility. Appliance wattages and usage hours are typical estimates.
A kilowatt (kW) is a unit of power — the rate at which energy is used at any given moment. A kilowatt-hour (kWh) is a unit of energy — the total amount consumed over time. A 2 kW electric heater running for 3 hours uses 6 kWh of energy (2 × 3 = 6). Your utility meter measures cumulative kWh, and your bill charges for total kWh consumed during the billing period.
The US average is approximately $0.16 per kWh according to the EIA, but rates vary dramatically by state and utility. Louisiana and Wyoming average around $0.10–$0.12/kWh, while Hawaii exceeds $0.35/kWh and California averages about $0.28/kWh. Many utilities also charge demand fees, time-of-use rates (cheaper at night), and tiered pricing that increases with usage.
Focus on the biggest consumers first: upgrade to a high-SEER air conditioner, install a heat pump water heater (uses 60% less energy), switch to LED lighting throughout the home, use ENERGY STAR appliances, and reduce phantom loads with smart power strips. A comprehensive home energy audit, often available free from utilities, identifies the highest-impact improvements for your specific situation.
Several factors cause discrepancies: appliances cycle on and off (refrigerators run about 8 hours out of 24), variable-speed motors adjust power usage, standby (vampire) power from electronics adds up (typically 5–10% of total usage), and seasonal factors affect heating/cooling loads. A whole-house power monitor provides the most accurate real-time tracking.
Divide your daily kWh usage by the peak sun hours in your area to get the required kW system size. For example, 30 kWh/day ÷ 5 peak sun hours = 6 kW system. Add 20–25% for system losses (inverter efficiency, shading, temperature derating). A 6 kW system needs approximately 15–18 panels rated at 350–400 watts each, per typical residential installations.
Convert power to energy in joules for scientific and engineering calculations.
Reverse conversion: determine power draw from energy consumption data.
Comprehensive tool to estimate electricity costs for any appliance or usage pattern.