Where 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.

What 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.

Does 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.

Why 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.

How 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.

EVEEveryday Life

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

Wattage

Hours per Day

Days per Month

days

Price per kWh

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How It Works

Formula

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

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

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

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

Where

$W$: Device wattage(W)
$h$: Hours of use per day(h)
$d$: Days of use per month(days)
$P$: 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.

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