CalcLibrary

Electricity Cost Calculator

Calculate how much it costs to run an appliance or device. Enter the wattage, hours per day, days per month, and your price per kWh — get the cost per month, per year, and per day, plus the kWh consumed. Useful for sizing a heater’s impact on the bill, comparing a new fridge against an old one, or estimating EV-charging costs.

Currency
W
h
days
$
Examples

A 9 W LED bulb running 8 hours a day for 30 days uses about 2.16 kWh/month and costs roughly $0.35/month at $0.16/kWh.

Cost per Month
$0.35
Cost per Year
$4.15
Cost per Day
$0.01
kWh per Month
2.16 kWh
kWh per Year
25.92 kWh

Light usage at 2.16 kWh/month — about a always-on small appliance or LED lighting. Yearly cost is roughly 4.15.

The default price per kWh is a rough placeholder, not an authoritative rate. Use the per-kWh figure from your utility bill for an accurate estimate.

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Examples

How It Works

Formula

kWh/month=W1000×h×d\text{kWh/month} = \dfrac{W}{1000} \times h \times d

Cost/month=kWh/month×P\text{Cost/month} = \text{kWh/month} \times P

Cost/year=Cost/month×12\text{Cost/year} = \text{Cost/month} \times 12

Cost/day=Cost/monthd\text{Cost/day} = \dfrac{\text{Cost/month}}{d}

Variables

WW

Device wattage(W)

hh

Hours of use per day(h)

dd

Days of use per month(days)

PP

Price per kilowatt-hour

Convert wattage to kilowatts (divide by 1,000). Multiply by hours-per-day and days-per-month for monthly kWh. Multiply monthly kWh by the price per kWh for monthly cost. Yearly figures are 12× the monthly values; daily cost is monthly cost divided by days-per-month.

Frequently Asked Questions

01Where do I find the wattage of a device?
Wattage is usually printed on a sticker or nameplate on the appliance itself, near the power cord, on the bottom, or on the back panel. The user manual lists it too. If only volts and amps are shown, multiply them: a 120 V × 12 A appliance draws about 1,440 W. For battery-charged devices, the rating on the charger is what matters when it is actually charging.
02What price per kWh should I use?
Use the per-kWh figure from your most recent utility bill — the default in this calculator is a rough placeholder, not an authoritative average. Rates vary by provider, tariff (fixed vs. time-of-use), region, and season, and have changed substantially in recent years. If your bill quotes a tiered or peak/off-peak rate, use the tier you actually fall into for the hours the device runs.
03Does this account for standby power?
No — the calculator assumes the device draws its rated wattage only while it is "on" for the hours-per-day you enter. Many electronics also draw a small standby current (often 0.5–5 W) the rest of the time. To include standby, run the calculator twice: once for active hours at full wattage, once for standby hours at the lower wattage, and add the costs together.
04Why does my appliance use less than its rated wattage?
The wattage on the label is the maximum draw the device can pull, not the average. A fridge cycles on and off — it might be rated 200 W but only run the compressor 30% of the time, averaging 60 W. A laptop drops to a fraction of its peak under light use. For cycling devices, multiplying rated wattage by hours overestimates consumption; a smart plug with energy logging gives a more accurate measurement.
05How do I compare an old appliance to a new one?
Run the calculator twice with the same hours-per-day and days-per-month figures, changing only the wattage. The difference in cost-per-year is the annual saving from upgrading. Compare that to the price difference between the two appliances to get a rough payback period — the same logic shop floors use when promoting energy-efficient models.

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