MultiConvers

Appliance Energy Cost Calculator

Estimate what one appliance costs to run over a day, a month and a 365-day year from nameplate watts, hours it is actually on each day, how many days you count in the month, and your unit price per kWh. The annual line does not clone a 30-day month twelve times.

Updated

How to use

  1. Enter power in watts from the label or a plug meter. A 100 W lamp is 0.1 kW.
  2. Enter hours per day the device is drawing that power — not 24 unless it truly never cycles off.
  3. Set days per month (often 30, at most 31) and the price per kWh from your bill’s unit rate.
  4. Read kWh/day, kWh/month, monthly cost, and the annual estimate. For a single session from watts × hours, use Electricity Cost instead.

How it works

Daily energy is (watts ÷ 1000) × hours per day. A 100 W lamp on five hours is 0.5 kWh/day. Monthly energy multiplies that by the days-per-month you typed. At 30 days and 0.20 per kWh the month is 15 kWh and 3.00. That path is for “this is how I use it most weeks,” not for a one-off boil.

Annual cost is 365 × daily kWh × price, so the same lamp is 36.50 a year at 0.20. It will not equal 12 × monthly cost when the month length is 30, because 12 × 30 is 360 days. The split is deliberate: monthly planning can use a 30-day convention; the year uses a civil 365 so February is not silently dropped twice.

Nameplate watts are a ceiling more often than a mean. A fridge marked 150 W does not pull 150 W all day — the compressor cycles. Entering 24 hours at 150 W will invent a huge bill. A plug-in kWh meter for a week, then hours-per-day back-calculated, is closer to reality. Heaters with thermostats and laptops that idle behave the same way.

The price should be the energy unit rate, not the whole-bill average that folds in standing charges. Time-of-use peaks need two runs (day rate and night rate) with different hours. Standing charges, taxes and VAT treatment are omitted.

Electricity Cost is one session: power × hours × price. kWh Cost is already-known kilowatt-hours × price. EV tools add battery percent and charger efficiency. This page is the daily-habit appliance identity.

Formula

kWh/day = (watts ÷ 1000) × hours/day
kWh/month = kWh/day × days/month
Cost/month = kWh/month × price
Annual cost = kWh/day × 365 × price

Worked examples

  • A 100 W lamp, 5 hours a day

    100 W, 5 h/day, 30 days, 0.20 / kWh → 0.5 kWh/day, 15 kWh/month, 3.00 / month

  • Same lamp, annual

    100 W, 5 h/day, 0.20 / kWh → annual cost 36.50 (365 × 0.5 × 0.20)

Useful notes

  • Annual cost uses 365 days, not 12 × your monthly days setting.
  • Rated watts may not equal average watts. Use a measured figure if you have one.
  • Days per month cannot exceed 31. Standing charges are not included.

FAQ

How do I estimate what an appliance costs per month?

kWh/day = (W ÷ 1000) × hours/day, then multiply by days in the month and by your kWh price.

Why doesn’t annual cost equal 12 × monthly cost?

Monthly cost uses the days/month you entered (often 30). Annual cost uses 365 days so a 30-day month is not silently treated as a 360-day year.

My fridge is 150 W. Do I enter 24 hours?

Only if the compressor truly runs all day. Duty cycle is often much lower. A measured kWh/day from a plug meter is better.

Can I enter 0 hours or 0 watts?

Yes. The identities still run; energy and cost become 0. Negative values are rejected.

How is this different from Electricity Cost?

Electricity Cost is one session (power × hours). This page repeats hours every day, then scales to a month and a 365-day year.

Guides

Related tools

See all Energy tools.

Sources