Electricity Cost Calculator

Estimate what any appliance or device costs to run based on its wattage, daily usage and your electricity rate.

Electricity Cost Calculator

Enter the device's power rating, how long it runs each day and your rate per kWh.
The running costs update live as you type.
For example, a 1,500 W heater used 5 hours a day at $0.22 per kWh costs about $49.50 a month.

Load an example

Device settings

Power consumption

The device's rating from its label.

Hours of usage per day

How long it runs each day (0–24).

Electricity rate per kWh

On your bill. Typical residential rates are about $0.10–$0.30 per kWh.

Projection period

How far ahead to project the cost.

Live mode

Recalculate automatically as you change any value. Turn this off to hold your results until you press the Calculate button.

Your Electricity Cost Result

Hourly cost

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Cost per day

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Period cost

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Energy used (period)

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Calculation breakdown Download

Fill in the device details and press Calculate to see a live, visual breakdown of the running cost.

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Overview

The Electricity Cost Calculator is a free online tool that estimates how much it costs to run any electrical device, from a phone charger to a space heater. You enter the device's power rating, how many hours a day it runs and the price you pay per kilowatt-hour, and the tool returns the hourly cost, the cost per day and the total cost for the period you choose, together with the energy consumed.

It is useful because appliance labels show watts, not money. Converting watts into running costs lets you find the power-hungry devices in your home, compare the running cost of two appliances before you buy, sanity-check an unexpectedly high electricity bill, or budget for something like a heater over winter. The tool is written in plain HTML, CSS and JavaScript using the site's shared Toolkit helper and Bootstrap for the layout, and every calculation happens locally in your browser – nothing you type is sent to any server.

What This Tool Does

You supply four things: the device's power consumption (in milliwatts, watts, kilowatts, megawatts or gigawatts), the hours of usage per day, your electricity rate per kWh, and the projection period (daily, weekly, monthly or yearly). The calculator then returns: • the cost of running the device for one hour; • the cost of running it for a full day; • the total projected cost over the period you selected; • the total energy consumed over that period in kilowatt-hours, the same unit your utility bills you in.

The built-in "Load an example" link fills the form with a typical space heater so you can see how the tool behaves in one click, and the Copy and Download buttons let you save the result as a formatted text file.

How the Calculation Works

The power rating is first converted to watts (1 kW = 1,000 W, 1 MW = 1,000,000 W, and so on), then multiplied by the daily usage hours to get the energy used each day in watt-hours. That daily energy is scaled by the period length and divided by 1,000 to convert to kilowatt-hours, and finally multiplied by your rate per kWh to give the cost. A month is treated as 30 days and a year as 365 days.

Cost = (power in W × hours per day × period days ÷ 1,000) × rate per kWh

The hourly cost is simply the power in kilowatts multiplied by the rate (1,500 W = 1.5 kW, so at $0.22/kWh that is $0.33 per hour). Very small hourly costs, like a 10 W router at $0.0015 per hour, are shown with extra decimal places so they never round down to $0.00. The worked examples in the next section follow these rules exactly.

Examples

Each example below was calculated with the exact formula this tool uses, so you can type the same numbers in and reproduce the result.

1. Gaming console – a console rated at 160 W played 4 hours a day at $0.17 per kWh, projected monthly. It burns 0.64 kWh per day, or 19.2 kWh over a 30-day month, so the hourly cost is about $0.03 and the monthly cost is $3.26 (about $0.11 per day).

2. Window air conditioner – a 1.2 kW unit (enter 1.2 with the kW unit selected) running 8 hours a day at $0.19 per kWh, projected yearly. That is 9.6 kWh per day, 3,504 kWh per year, an hourly cost of $0.23, a daily cost of $1.82 and a yearly cost of $665.76 – the kind of number that makes a thermostat schedule look very attractive.

3. Laptop charger – a 65 W charger plugged in 10 hours a day at $0.28 per kWh, projected weekly. The hourly cost is $0.02, each day uses 0.65 kWh costing $0.18, and a full week adds up to 4.55 kWh or $1.27.

4. Irrigation pump – a 30 kW farm pump (enter 30 with the kW unit selected) running 6 hours a day at $0.09 per kWh, projected daily. Every hour on the pump costs $2.70, and one day of watering uses 180 kWh for $16.20.

5. Server rack – an 8 kW rack (enter 8 with the kW unit selected) running 24 hours a day at $0.11 per kWh, projected monthly. It draws 192 kWh every day, so a 30-day month totals 5,760 kWh and $633.60, with an hourly cost of $0.88.

Conversion Details

The calculator never mixes units. Whatever unit you pick is converted to watts first, so 1.2 kW, 1,200 W and 1,200,000 mW all produce exactly the same numbers.

Power unit conversions:
• 1 milliwatt (mW) = 0.001 W
• 1 watt (W) = 1 W (the base unit)
• 1 kilowatt (kW) = 1,000 W
• 1 megawatt (MW) = 1,000,000 W
• 1 gigawatt (GW) = 1,000,000,000 W

Cost calculation formula:
• Daily energy (Wh) = power (W) × hours of usage per day
• Projected energy (Wh) = daily energy × period days
• Projected energy (kWh) = projected energy (Wh) ÷ 1,000
• Cost = projected energy (kWh) × electricity rate ($/kWh)

Period multipliers:
• Daily = 1 day
• Weekly = 7 days
• Monthly = 30 days
• Yearly = 365 days

Costs of one cent or more are rounded to two decimal places; anything smaller keeps four decimal places, so genuinely cheap devices, such as a router, still show a meaningful number instead of $0.00.

FAQs

FAQ 1: Where do I find the wattage of my device?
Answer: Most appliances print the power rating in watts (W) on a label on the back or underside, on the plug-in power brick, or in the manual's specifications. If the label lists volts and amps instead, multiply them together to get watts. For something like a laptop charger rated at 65 W, enter 65.

FAQ 2: What is a kWh and where do I find my rate?
Answer: A kilowatt-hour (kWh) is the energy a 1,000 W device uses in one hour, and it is the unit your electricity supplier bills you in. Your rate is printed on your utility bill or in your online account, usually as a price per kWh. If you cannot find it, most residential rates fall between $0.10 and $0.30 per kWh.

FAQ 3: Why does a month use 30 days and not the calendar length?
Answer: The calculator projects every month as 30 days so that results are consistent and easy to compare between devices. Over a whole year this averages out (30 × 12 = 360 days versus 365 actual days), so for long-term budgeting use the yearly projection, which uses the full 365 days.

FAQ 4: Does the result include taxes and fixed supply charges?
Answer: No. The calculation uses only the rate per kWh you enter. Taxes, standing charges and tiered pricing are not included, so if your bill has those extras, either add them to the rate or treat the result as the energy portion of your bill only.

FAQ 5: Does the tool account for devices that cycle on and off?
Answer: Not directly – it assumes the device draws its full rated power for every hour you enter. Devices with thermostats, like fridges, heaters and air conditioners, actually run at their rated power only part of the time. For those, enter an effective number of hours (for example, a heater cycling 50% of the time for 10 hours counts as 5 hours).

FAQ 6: Is my data sent anywhere?
Answer: No. The calculator runs entirely in your browser using JavaScript, and no input or result is transmitted, logged or stored. You can even use it offline once the page has loaded.