Tech calculator
Device Electricity Cost Calculator
Estimate daily, monthly, and annual electricity costs from device wattage, usage time, and utility rates.
Monthly cost
$3.6
How device electricity cost works
The calculator estimates the energy a device consumes and its cost. Device wattage is the power rating, typically printed on the device label or power adapter; it represents the constant energy draw in watts. Hours per day is capped at 24, and days per month is capped at 31, to prevent physically impossible input. The electricity rate is measured in dollars per kilowatt-hour (the standard billing unit from utility companies). All inputs must be non-negative numbers, and the calculator validates that hours per day do not exceed 24 before computing results.
The main output shows monthly cost in dollars, calculated by first converting the energy consumption to kilowatt-hours, then multiplying by the rate. Three detail rows show the monthly energy consumption in kWh, the daily cost (monthly cost divided by days per month), and the annual cost (monthly cost multiplied by 12). The monthly kWh becomes the foundation for all three cost outputs, so accuracy in wattage and usage time is essential.
Worked example: 100 W device, 8 hours per day, 30 days per month
A 100 W device uses 0.1 kW. Running 8 hours per day for 30 days: 0.1 × 8 × 30 = 24 kWh per month. At an electricity rate of $0.15 per kWh, the monthly cost is 24 × 0.15 = $3.60. The daily cost is $3.60 ÷ 30 = $0.12, and the annual cost is $3.60 × 12 = $43.20.
This example matches a modest device, like a large TV or a desktop monitor pair. Over a year, even at this low wattage, electricity costs add up to $43.20 before tax or fixed charges. Scaling to a 1,000 W device would multiply all costs by 10, making it $432 annually. The daily cost row helps with budgeting, since $0.12 per day is roughly $3.60 per month in visible charges.
High-power appliances and surprising costs
A central air conditioning system typically draws 3,500 to 5,000 W. Running at 4,000 W for 8 hours daily across a 31-day summer month consumes 992 kWh. At $0.15 per kWh, a single month costs $148.80, or $1,785.60 annually. Peak summer months with 10 to 12 hours of air conditioning can easily double this. Utilities offer lower night rates in some regions; entering a blended rate will account for this.
Electric water heaters draw a lot when active but cycle on and off. A 4,500 W element that actively heats about 3 hours a day uses 4.5 × 3 × 30 = 405 kWh in a 30-day month, about $60.75 at $0.15 per kWh, which makes it one of the largest single loads in many homes. Entering 24 hours instead would model the worst case of an element stuck on: 3,240 kWh and $486 for the month. At the other end of the scale, a 65 W laptop adapter charging 4 hours a day uses 65 ÷ 1,000 × 4 × 30 = 7.8 kWh, about $1.17 per month.
Real-world usage patterns and cost examples
- Desktop computer (500 W) used 8 hours per day for 30 days: 500 ÷ 1,000 × 8 × 30 = 120 kWh, costing $18 per month at $0.15 per kWh.
- Gaming console (180 W) used 5 hours per day for 30 days: 180 ÷ 1,000 × 5 × 30 = 27 kWh, costing $4.05 per month.
- Refrigerator (150 W) running 24 hours per day for 31 days: 150 ÷ 1,000 × 24 × 31 = 111.6 kWh, costing $16.74 per month. This is always-on, so it contributes to baseline electricity even when no one is home.
- Electric oven (3,000 W) used 1 hour per day for 30 days: 3,000 ÷ 1,000 × 1 × 30 = 90 kWh, costing $13.50 per month.
- Programmable coffee maker (800 W) used 1 hour per day for 30 days: 800 ÷ 1,000 × 1 × 30 = 24 kWh, costing $3.60 per month. If left on standby instead, the cost would drop significantly.
Frequently asked questions
Where do I find the wattage of a device?
Check the power label on the device itself, usually printed on the back or bottom. On appliances with cords, look for a label near the plug or on the device body. For devices with external power adapters, the wattage is printed on the adapter brick. If unavailable, search the model number and manufacturer online for the spec sheet.
My device has a variable power draw. Should I estimate an average?
Yes. A microwave might peak at 1,000 W but is rarely at full power. A laptop charger delivers different power depending on whether the device is charging or idle. Use the highest typical power draw if you want a conservative estimate, or research the average load for that device type.
Why is there a cap at 24 hours per day and 31 days per month?
A day has exactly 24 hours, so 24 is the physical maximum. Months vary from 28 to 31 days; 31 is the longest, so it's the calculator's ceiling. You can enter 28, 29, or 30 to match the actual calendar month for more precision.
How do I adjust for different electricity rates?
Find your electricity rate on your utility bill, where it is usually listed as cents per kWh. The calculator accepts dollars per kWh, so convert 15 cents per kWh to $0.15. Rates vary by region, time of day, and season; enter the rate that applies to your usage pattern.
If I turn off a device, does standby power still cost money?
Standby draw depends on the device. Modern TVs might use 2 to 5 W when powered off but plugged in; older devices can draw 10 W or more. The calculator will show the cost of this phantom load if you enter the wattage and set daily hours to the fraction when it is in standby mode. Unplugging devices completely eliminates standby cost.
How accurate is this estimate compared to my actual electric bill?
This calculator estimates individual device cost but not total household cost. Your bill includes all devices, fixed charges, taxes, and seasonal rate variations. Use this calculator to understand which devices contribute most to your bill, then verify against actual usage by checking your meter or smart home monitor over time.