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.

Examples

LED bulb

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.

Wattage: 9 W
Hours per Day: 8 h
Days per Month: 30 days
Price per kWh: $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

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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}

Variables, symbols and units

$W$: Device wattage(W)
$h$: Hours of use per day(h)
$d$: Days of use per month(days)
$P$: Price per kilowatt-hour

Calculation method explained

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.

References and source material

Examples

LED bulb9 W · 8 h → $0.35

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.

Wattage: 9 W
Hours per Day: 8 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $0.35

Router12 W · 24 h → $1.38

A 12 W router running 24 hours a day for 30 days uses about 8.64 kWh/month and costs roughly $1.38/month.

Wattage: 12 W
Hours per Day: 24 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $1.38

Laptop65 W · 8 h → $1.83

A 65 W laptop used 8 hours a day for 22 days uses about 11.44 kWh/month and costs roughly $1.83/month.

Wattage: 65 W
Hours per Day: 8 h
Days per Month: 22 days
Price per kWh: $0.16 /kWh

Cost per Month: $1.83

Refrigerator60 W · 24 h → $6.91

A refrigerator averaging 60 W around the clock uses about 43.2 kWh/month and costs roughly $6.91/month.

Wattage: 60 W
Hours per Day: 24 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $6.91

Microwave1,200 W · 0.25 h → $1.44

A 1,200 W microwave used 0.25 hours a day for 30 days uses about 9 kWh/month and costs roughly $1.44/month.

Wattage: 1,200 W
Hours per Day: 0.25 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $1.44

Air fryer1,200 W · 0.5 h → $1.92

A 1,200 W air fryer used 0.5 hours a day for 20 days uses about 12 kWh/month and costs roughly $1.92/month.

Wattage: 1,200 W
Hours per Day: 0.5 h
Days per Month: 20 days
Price per kWh: $0.16 /kWh

Cost per Month: $1.92

Fan50 W · 10 h → $2.40

A 50 W fan used 10 hours a day for 30 days uses about 15 kWh/month and costs roughly $2.40/month.

Wattage: 50 W
Hours per Day: 10 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $2.40

Space heater1,500 W · 4 h → $28.80

A 1,500 W space heater used 4 hours a day for 30 days uses about 180 kWh/month and costs roughly $28.80/month.

Wattage: 1,500 W
Hours per Day: 4 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $28.80

Dehumidifier300 W · 8 h → $11.52

A 300 W dehumidifier used 8 hours a day for 30 days uses about 72 kWh/month and costs roughly $11.52/month.

Wattage: 300 W
Hours per Day: 8 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $11.52

TV120 W · 5 h → $2.88

A 120 W TV used 5 hours a day for 30 days uses about 18 kWh/month and costs roughly $2.88/month.

Wattage: 120 W
Hours per Day: 5 h
Days per Month: 30 days
Price per kWh: $0.16 /kWh

Cost per Month: $2.88

Desktop PC450 W · 4 h → $7.49

A 450 W desktop PC used 4 hours a day for 26 days uses about 46.8 kWh/month and costs roughly $7.49/month.

Wattage: 450 W
Hours per Day: 4 h
Days per Month: 26 days
Price per kWh: $0.16 /kWh

Cost per Month: $7.49

EV charger7,400 W · 2 h → $47.36

A 7,400 W EV charger used 2 hours a day for 20 days uses about 296 kWh/month and costs roughly $47.36/month.

Wattage: 7,400 W
Hours per Day: 2 h
Days per Month: 20 days
Price per kWh: $0.16 /kWh

Cost per Month: $47.36

Frequently Asked Questions

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.

Electricity Cost Calculator

LED bulb

How It Works

Examples

Frequently Asked Questions

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