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Electricity Cost Calculator

What an appliance costs to run — per day, month or year, including the standby draw nobody counts.

Enter the wattage, how long it runs, and your electricity price.

From the label or the manual. This is the maximum draw, not the average.

On your electricity bill. The US average is around $0.17.

Standby draw

What it pulls while idle. A few watts around the clock adds up, and it applies for the hours the device is not in use.

Estimate. A real-world figure based on the assumptions listed below, which you can change.

How this calculator works

Watts times hours, divided by a thousand, gives kilowatt-hours. Multiply by your price per kWh and you have the cost. A 1,500 W heater running five hours a day uses 7.5 kWh — around $1.28 at seventeen cents.

The catch is that the number on the label is the maximum draw, not the average. Anything on a thermostat cycles: a space heater on a cold day might run half the time, a fridge far less than that. This calculates what the figure you enter would cost and says plainly that the label overstates it, rather than applying a duty-cycle guess that would be wrong for every appliance except one.

Standby is the number people miss. A device pulling three watts continuously uses 26 kWh a year — trivial alone, and not trivial across the fifteen or twenty things in a house that never fully switch off. It is a separate field because it applies for the hours the device is not in use, and multiplying it by a full 24 is the error the field exists to prevent.

Whatever period you pick, the daily, monthly and annual costs are all shown, because the annual figure is usually the one that changes a decision.

The formula

Exactly what happens to your numbers, step by step.

  1. Energy

    kWh = watts × hours ÷ 1,000

  2. Cost

    cost = kWh × price per kWh

  3. Standby

    standby kWh = standby watts × (24 − hours in use) ÷ 1,000

    Only for the hours it is idle.

A worked example

A 1,500 W space heater running 5 hours a day at $0.17 per kWh.

What you enter

Power
1,500 W
Hours a day
5
Price
$0.17 per kWh

The working

Energy a day
1,500 × 5 ÷ 1,000 = 7.5 kWh
Cost a day
7.5 × $0.17 = $1.28
A month
$38.81
A winter, roughly
$155

$1.28 a day — about $39 a month

Worth knowing before the bill arrives. And worth remembering that a thermostat means the real figure is lower: a heater that cycles half the time costs about half this, which is exactly why the label number should be treated as a ceiling.

Assumptions

Every result here rests on these. Change your inputs and the result changes with them.

  • The device draws its rated wattage for the whole time it is in use.
  • Standby draw applies for every hour it is not in use.
  • Your price per kWh is the all-in rate including delivery charges.
  • A month is 30.44 days and a year 365.25, so the periods stay consistent.

What this cannot tell you

  • The label rating is a maximum. Anything thermostat-controlled — heaters, fridges, air conditioning, ovens — cycles on and off, and its real consumption is well below the figure on the plate.
  • Electricity pricing is often not a single rate. Tiered pricing, time-of-use rates and demand charges all mean the marginal cost of another kilowatt-hour may differ from your average.
  • Motors and compressors draw a surge on startup that this does not model. It matters for sizing a circuit, not usually for a bill.
  • A plug-in energy monitor measures what a device actually uses. Where a decision depends on the number, that beats any calculation from a label.

Questions people ask

How do I work out what an appliance costs to run?

Multiply the watts by the hours used, divide by 1,000 for kilowatt-hours, then multiply by your price per kWh. A 100 W device for 8 hours is 0.8 kWh — about 14 cents at seventeen cents a unit.

What is the average price per kWh?

It varies enormously by state and by supplier. The US average is around seventeen cents, but the figure on your own bill is the only one worth using — divide the total by the kilowatt-hours to get your true all-in rate.

Does standby power actually matter?

Individually, barely. Collectively, yes: a few watts each across every television, console, charger and smart speaker in a house adds up to a real share of a bill, and it is being spent on nothing.

Why is my bill higher than this suggests?

This costs one appliance. A bill is everything at once, plus fixed supply charges, and possibly a tiered rate where later kilowatt-hours cost more than early ones. It is a tool for comparing devices rather than predicting a bill.

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Sources and review

The default figures here are typical published values, not fixed constants — densities, coverage rates and rules of thumb vary by product and by supplier. Every one of them is an input you can replace, and the figure on your supplier’s quote or the manufacturer’s data sheet beats any default. The assumptions and limitations above set out exactly what this rests on.

Methodology version 1.0.0 · Last reviewed