wattwise.
SMALL NUMBERS. SMARTER CHOICES.

Electricity cost calculator.

Know what your appliances really cost.
Turn watts and hours into a clearer picture of your energy use.

✓ Free to use✓ No signup✓ Calculated in your browser
01 / YOUR INPUTS

A few details. That's it.

$
days

Use the price per kWh on your electricity bill. 0.16 is an example rate, not a live tariff. Changing currency only changes the label.

Your appliances

1 appliance
QUICK ADD

Preset wattages are illustrative. Check the appliance label or measured average power. For appliances that cycle on and off, enter equivalent full-power hours.

No account needed
THE MATH, MADE SIMPLE

From watts to
what you pay.

A kilowatt-hour (kWh) is a unit of energy. An appliance running at 1,000 watts for one hour uses 1 kWh.

Try your own numbers ↗
THE ELECTRICITY COST FORMULA

Watts ÷ 1,000 × hours × rate per kWh

= cost per day, for one appliance
  1. 01

    Find the wattage

    Look at your appliance label or manual. If it lists kilowatts (kW), multiply by 1,000 to get watts.

  2. 02

    Estimate daily use

    Use average running time, including partial hours. Multiply by the number of identical appliances.

  3. 03

    Use your own electricity rate

    Multiply daily kWh by your price per kWh, then by the number of days. For cents per kWh, divide by 100 first.

PUT IT IN PERSPECTIVE

Little habits. Different costs.

Example estimates at $0.16/kWh,
for 30 days. Your usage will vary.

Space heater

1,500 W · 4 hours/day

$28.80 / month

Desktop computer

300 W · 6 hours/day

$8.64 / month

LED light bulb

10 W · 5 hours/day

$0.24 / month
A LITTLE MORE CLARITY

Good questions.
Clear answers.

How do I calculate an appliance's electricity cost?

Divide watts by 1,000, multiply by daily operating hours, then multiply by your electricity rate per kWh. For example, a 1,500 W heater used 4 hours a day consumes 6 kWh per day. At $0.16/kWh, that is $0.96 per day or $28.80 for 30 days.

Will this match my electricity bill?

This calculates the usage cost of the appliances you enter. Your bill may also include standing charges, taxes, other appliances, or rates that change with usage or time of day. To estimate an entire bill, account for those items separately.

What is the difference between watts and kWh?

Watts measure power at a moment in time. Kilowatt-hours measure energy used over time. A 100 W appliance running for 10 hours consumes 1 kWh, as does a 1,000 W appliance running for one hour.

How should I estimate a refrigerator or air conditioner?

These appliances cycle on and off and may draw different amounts of power while running. Use measured average power, the manufacturer's energy consumption figure, or equivalent full-power hours. Annual kWh from an energy label divided by 365 gives a daily energy estimate. Rated watts multiplied by 24 hours will often overestimate consumption.

Does changing currency convert the electricity rate?

No. It changes how the costs are displayed. Enter your rate in the currency selected. For example, if your bill says 25 pence per kWh, choose GBP and enter 0.25.

Are my calculator inputs stored?

Calculations run in your browser. Settings are saved in this browser only if you check “Remember my settings.” Shared links contain your calculator inputs, so anyone with that link can read them. This version has no analytics, advertising, or account signup.

A clearer view of your energy.
One appliance at a time.

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