Electricity Cost Calculator — Free Online Calculator & Formula Guide

How Electricity Cost Works

Cost = (Watts × Hours/Day × Days) / 1000 × $/kWh × Quantity

Calculate the energy cost of any electrical appliance. First find kilowatt-hours (kWh), then multiply by your electricity rate.

W × h

Wattage & Usage — Power rating in Watts multiplied by hours of use per day. The foundation of energy consumption calculation.

d

Number of Days — Billing period or time span to calculate over.

¢

Cost per kWh — Your electricity rate in cents per kilowatt-hour. Found on your electric bill.

How to Use

1. Select an appliance from the Quick Select list to auto-fill wattage, or enter a custom value.
2. Enter the average hours of use per day.
3. Choose a period (Day, Week, Month, or Year) or use the default 30-day calculation.
4. Enter your electricity rate in $/kWh (US average is ~$0.14).
5. Set the number of identical appliances (e.g., 10 LED bulbs).

Understanding the Result

Electricity is billed per kilowatt-hour (kWh), which represents 1,000 watts used for one hour. This calculator converts appliance wattage to kilowatt-hours, multiplies by your local electricity rate, and projects costs over daily, monthly, and yearly periods. Understanding appliance energy costs helps you identify energy-saving opportunities and manage your electric bill. Practical example: a gaming PC drawing 500W used for 6 hours per day. Daily consumption: (500 × 6) / 1000 = 3 kWh. At $0.14/kWh, daily cost = $0.42, monthly cost (30 days) = $12.60, yearly cost = $153.30. Compare with an LED TV (120W) used 6 hours: 0.72 kWh/day, $0.10/day, $3.02/month, $36.74/year. The gaming PC costs over 4 times more to run. Edge cases: for appliances with variable power draw, such as refrigerators and air conditioners that cycle on and off, the nameplate wattage overestimates actual consumption — a refrigerator rated at 700W typically runs only about 30% of the time, averaging 210W. Use a plug-in power meter (like a Kill-A-Watt) for accurate measurements. For electric vehicle charging at Level 2 (7,000W for 4 hours), consumption is 28 kWh/day, costing $3.92/day, $117.60/month, $1,430.80/year. Time-of-use billing can significantly affect costs — charging overnight at off-peak rates (potentially $0.08/kWh) versus peak rates ($0.30/kWh) can cut EV charging costs by 70%. For standby power (vampire power), devices like cable boxes, game consoles, and phone chargers draw 1-10W continuously — 10 such devices at 5W each, 24/7, costs about $0.50/month at average rates, or $6/year in wasted energy.

Frequently Asked Questions

What is a kilowatt-hour (kWh)?

A kilowatt-hour is a unit of energy equal to using 1,000 watts for one hour. If a 100W light bulb runs for 10 hours, it uses 1 kWh. Your electric bill charges you per kWh consumed.

What is the average US electricity rate?

As of recent data, the US average residential electricity rate is approximately $0.14 per kWh. Rates vary significantly by state — from under $0.10 in some states to over $0.30 in others (e.g., Hawaii, California).

How can I reduce my electricity bill?

Replace incandescent bulbs with LEDs, unplug devices when not in use, use smart power strips, run major appliances during off-peak hours, maintain HVAC systems, improve home insulation, and consider energy-efficient appliances (look for ENERGY STAR ratings).

Sources

• Electricity Pricing
• Electricity Cost