CalcaTools

Electricity Calculator | Calculate Appliance Energy Use and Cost

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Calculate what your appliances cost to run from wattage, daily usage and your electricity rate — daily, monthly and yearly totals. Audit your home's energy use and find the biggest savings in your bill.

Last updated: June 2026 · Free · No sign-up required

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Results

Enter values above and click Calculate to see your result instantly.

Quick reference

ApplianceWattsDaily cost @ $0.15
LED bulb10 W$0.01 (8 h)
Fridge150 W$0.54 (24 h)
Space heater1,500 W$0.90 (4 h)

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Every tool is plain HTML + JavaScript with the calculation logic compiled in. No spinner, no "verifying browser" splash, no five-second wait while ads load. Hit the page, fill the form, get the answer. Slow tools waste your time and ours.

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Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.

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Interpretation guide

OutputWhat it tells you
Daily costWhat the appliance costs to run each day.
kWh usedEnergy consumed per day (watts × hours ÷ 1000).
Scale upMultiply daily cost by 30 or 365 for monthly or yearly.

lightbulb Worked example — the true cost of a space heater

A 1,500 W space heater runs 6 hours a day; electricity costs $0.16/kWh. Daily energy = 1.5 kW × 6 h = 9 kWh. Daily cost = 9 × $0.16 = $1.44.

Result: $1.44 per day — about $43 a month.

What this means: That single heater costs more per month than a modern fridge ($5–10). Cutting run time to 3 hours with a timer halves the bill, which is why a $15 timer plug pays for itself in the first month.

Formula & methodology

Formula: Cost = (watts ÷ 1000) × hours per day × rate per kWh

How running cost is calculated

Energy in kilowatt-hours = power in watts ÷ 1,000 × hours used. Cost = energy × your rate per kWh.

  • Daily: (watts ÷ 1,000) × hours × rate.
  • Monthly: daily × 30; yearly: daily × 365.

For appliances that cycle on and off (fridges, thermostat heaters), use the average draw rather than the nameplate rating — a 150 W fridge may average only 50 W across the day.

Authoritative source: timeanddate.com

Frequently asked questions

How do I calculate electricity cost?
Yes — the Electricity Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
What is a kilowatt-hour?
The Electricity Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Works out how much any electrical appliance costs to run. Enter the appliance's wattage, how many hours per day you use it, and your electricity rate per kWh, and the tool calculates the daily, monthly, and yearly running cost, plus the annual energy use in There is no limit on usage, and it works on any device.
How do I find my electricity rate?
Enter the required values into the input fields and press the calculate button. The tool applies the formula Cost = (watts ÷ 1000) × hours per day × rate per kWh and returns the result with a short explanation of each step, so you can check the working yourself.
How do I get the monthly or yearly cost?
Multiply the daily cost by 30 for a typical monthly estimate and by 365 for the yearly figure. The calculator shows all three: daily, monthly, and yearly running cost. A device costing $0.90 per day adds up to about $27 monthly and $329 yearly, which is why small wattage differences compound into meaningful annual bills.
Is it free and private to use?
Yes — the calculator is completely free with no sign-up or limits, and all calculations run in your browser so your appliance data is never uploaded. CalcaTools covers its costs with display advertising. Use it to audit your appliances without creating an account or sharing personal information.
What if my appliance cycles on and off, like a fridge?
Use its average power draw, not the nameplate rating. A fridge rated 150 W might average 50 W over a day because the compressor cycles. Check an energy monitor or smart plug for the real average — or estimate duty cycle (runs one-third of the time → 150 × 0.33 ≈ 50 W).
Why divide watts by 1,000?
Because electricity is billed in kilowatt-hours, and kilo means 1,000. A 1,500 W heater is 1.5 kW; run it one hour and you have used 1.5 kWh. The division just converts the appliance's watt rating into the billing unit.
Is my data sent anywhere when I calculate?
No — the math runs on the page itself, so your appliance and usage details never leave your device.
How precise is the cost estimate?
The formula is exact; accuracy hinges on two inputs: the wattage (nameplate ratings can be 10–20% off real draw) and your tariff (time-of-use rates vary by hour). For a planning estimate it is well within ±15%; a plug-in meter gives the true number.

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