SizingKitEnergy & cost
Electricity cost calculator
A 480 W dehumidifier run nine hours a day through a 150-day season uses 648 kWh, and the 3 W it keeps drawing for the other 7,410 hours of the year adds 22.2 more — 670 kWh in all, which is the figure a rate gets multiplied by. This page prices one machine rather than a building: running draw and standby draw are separate lines, the year is 8,760 hours and the month is 730 rather than a rounded 720, and a second column takes whatever you would put in its place so the annual difference and the payback land side by side. It supplies no electricity rate of its own: that figure comes off your own bill, because a national average is wrong for everybody who actually has a utility.
- 100% free
- No signup
- Standby as its own line
- Two appliances compared
- Payback in years
The appliance, and the one you would put in its place
Leave the second column empty to price a single machine. Standby is what it draws when it is finished and still plugged in, and it is almost never on the nameplate — a plug-in meter reads it in about ten seconds.
| Field | This one | Instead of it |
|---|---|---|
| What it is | ||
| Power while running | ||
| Hours it runs a day | ||
| Days a year it is used | ||
| Standby power | ||
| Price to buy it |
Power fields take any unit written into them, so a 5,100 BTU/h window unit and a 1.5 kW heater both read. 0.50 W is the ceiling for what may be sold into the EU in plain standby — Commission Regulation (EC) No 1275/2008 as amended by (EU) No 801/2013, off mode and standby, measured to IEC 62301. Equipment carrying an information or status display is allowed 1.00 W under the same article.
Divide the amount your last bill charged for energy by the kilowatt-hours that bill covered. Taxes, delivery and a fixed customer charge belong in that division only if you want the figure this appliance really adds to the total.
What this appliance costs
KILOWATT-HOURS A YEAR
670 kWh
COST A YEAR
—
| Horizon | Dehumidifier, 50 pint |
|---|---|
| One hour while it runs | 0.48 kWh |
| One average day | 1.84 kWh |
| One month, 730 hours | 55.9 kWh |
| One year, 8,760 hours | 670 kWh |
| Of that year, standby alone | 22.2 kWh |
- Draw while running
- 480 W · 1,638 BTU/h
- A year of it as heat
- 2,413 MJ
- Hours idle but plugged in
- 7,410 h
- Standby share of the year
- 3.32%
What put the kilowatt-hours here: Running did — 648 kWh over 1,350 hours against 22.2 kWh of standby, which is 3.32% of the total. Hours per day is the field to argue about, and it is the one people overstate.
What this arithmetic assumes. That the appliance draws its rated power the whole time it is on. Anything with a thermostat, a compressor or a variable-speed motor does not: it cycles, and the number you want is the average over an hour rather than the peak on the plate. A clamp meter or a plug-in energy monitor left on it for a day settles that question and nothing on this page can.
How to price one appliance, including the hours it is doing nothing
Three fields decide the answer and only one of them is printed on the machine.
Take the running draw, and be suspicious of the plate
The nameplate figure is what the appliance draws at full tilt. A resistive load — a kettle, a toaster, a resistance heater — really does draw it the whole time it is on, so the plate is the answer. Anything with a compressor, a thermostat or a variable-speed motor does not: it cycles, and the number this page wants is the average across an hour. A plug-in energy monitor left on it overnight settles that in a way no specification sheet can.
Split the hours into running and idle
Enter the hours a day it actually runs and the days a year it is used, and the page works out the rest of the year for you. A seasonal machine is the interesting case: nine hours a day for 150 days is 1,350 running hours, which leaves 7,410 hours in which the appliance is doing nothing and still drawing its standby watts. Measure that standby figure too — almost nothing states it, and it is the reason two appliances with the same plate can differ by a hundred kilowatt-hours a year.
Put the replacement in the second column
Fill in the machine you are thinking of buying and its price, and the page returns the annual saving and how many years the extra purchase price takes to come back through the meter. Read that payback against the remaining life of the equipment rather than against how long you plan to stay: a nine-year payback on a machine with six years left in it is a purchase justified by something other than electricity.
Technical specifications
| Power fields | Any unit written into them reads: 1.5 kW, 5,100 BTU/h and 0.75 hp all arrive as watts, and the standby field takes the same. Zero is a legal standby figure for anything with a hard switch on the primary side. |
|---|---|
| How idle hours are found | Whatever the running hours leave over. Nine hours a day across 150 days is 1,350 running hours, so standby holds the remaining 7,410 of the year — the page never asks you to work that subtraction out. |
| The month it uses | 730 hours, one twelfth of 8,760. Calculators that call a month 720 hours understate every monthly figure by 1.4%, and no utility bills on either — a meter-read cycle normally lands between 28 and 34 days. |
| Leap years | Not modeled. A leap year is 8,784 hours, 0.27% more, which is an order of magnitude smaller than the uncertainty in the hours you entered. |
| The standby limit quoted | 0.50 W in off mode and plain standby, 1.00 W where there is an information or status display, under Commission Regulation (EC) No 1275/2008 as amended by (EU) No 801/2013, measured to IEC 62301. Networked standby is allowed more under the same article, and networked standby is where the watts usually are. |
| The comparison | Both columns priced against one rate, returning the annual difference and a payback in whole tenths of a year from the two purchase prices. No discount rate, no price escalation and no residual value — it is division, and it is labeled as division. |
| Where the rate comes from | One field, in dollars per kilowatt-hour, empty until you fill it. Every kilowatt-hour figure on the page is reported without it, so the energy answer stands whether or not you know what you pay. |
| What leaves the browser | Nothing. Both appliance columns, the two prices and the rate are multiplied in the tab and gone on reload. |
Frequently asked questions
Why is the cost for one hour not the daily cost divided by 24?
Because they are hours of different kinds. The hourly figure is a running hour — the machine working, drawing its full load — while the daily figure is an average across a whole day in which it mostly is not. A 480 W dehumidifier uses 0.48 kWh for every hour it runs and averages 1.84 kWh a day over a year, and dividing that second figure by 24 would describe an appliance drawing 76.5 W continuously, which is nothing that exists.
Is standby power actually worth counting?
For anything that spends most of the year idle, yes, and the arithmetic is blunt about it: a games console left in networked standby at 10 W draws 87.6 kWh over a year, while a 1,200 W microwave used six minutes a day draws 43.8 kWh. The console is doing nothing for all 8,760 of those hours and still uses twice as much as the microwave doing its job. Standby is small multiplied by enormous, and it is the term people leave out.
My appliance is rated in amps. How do I get watts?
Multiply volts by amps, and then stop if the load is resistive. A 1,500 W space heater on a 120 V circuit really does draw 12.5 A, because a heating element has a power factor of one. A motor does not: its nameplate current includes reactive current that does no work, so volts times amps overstates the watts a meter registers. Working out which figure you have is what the volts amps watts calculator and the power factor calculator are for.
Does the appliance heat the room, and does that cost extra?
Every watt an appliance draws leaves it as heat, so a 480 W machine is also a 1,638 BTU/h heater standing in the room. In winter that is heat you were going to pay for anyway, and it displaces whatever your heating system would have burned. In a cooled space it is worse than it looks: the air conditioner has to remove that heat as well, and it does so at its own efficiency, so a watt of appliance costs you a watt plus roughly a third of a watt more at the compressor.
How long is a payback allowed to be before it stops being worth it?
Shorter than the remaining life of the machine, which is the comparison this page can help with and the only one it can. A dryer that saves eleven dollars a year cannot repay a four-hundred-dollar price difference inside anything a manufacturer would warrant, and the figure this page returns says so plainly rather than dressing it up. Where the difference is close, the honest tiebreakers are the ones no calculator holds: warranty length, whether parts are still made, and how much of your own time a failure costs.
Why did the standby figure change when I only edited days per year?
Because the two are the same 8,760 hours divided differently. Days per year and hours per day together fix how long the appliance runs, and everything left over is time it spends idle and plugged in — so cutting the season from 150 days to 100 removes 450 running hours and hands them straight to the standby line. That is the point of entering the two states separately: the total is fixed by the calendar and only the split is yours.
Can I use this for a three-phase machine in a workshop?
Yes, as long as the figure you enter is real power in watts or kilowatts rather than kVA. A three-phase motor's nameplate usually gives amps at a voltage, and turning that into watts needs the square root of three and the power factor — do that first, on the three phase power calculator, and bring the kW figure here. Everything downstream of the watts on this page is phase-agnostic, because a kilowatt-hour is a kilowatt-hour however it arrived.
About running cost, and why standby is the term that surprises people
An appliance has two power states and almost every calculator models one of them. The running state is easy and is printed on the machine; the idle state is neither, and it is where the arithmetic turns over. What makes it turn over is not the size of the draw but the size of the multiplier: a running load is multiplied by the hundreds or low thousands of hours it actually works, while a standby load is multiplied by everything else, and everything else is most of 8,760. That is why a 3 W transformer humming inside a device can be a rounding error and a 10 W networked standby can beat the appliance it belongs to. The same shape explains a piece of equipment far from any kitchen: a distribution transformer's core loss is a continuous draw that runs whether the building is occupied or not, which is why it is weighed against copper loss when you size a transformer rather than treated as a detail.
The other thing this page insists on is that hours are not calendar hours. A month here is 730 hours because a year is 8,760 and there are twelve of them; the widely used 720 comes from calling every month thirty days and it makes monthly figures 1.4% too small. Your utility uses neither, because it bills on the interval between two meter reads, which drifts between twenty-eight and thirty-four days and is why two bills for identical use are never the same. If you want to reconcile any of this against a real bill, the arithmetic has to move to the bill's own period and its own structure: that is what the kwh cost calculator does with the tariff, and what the energy usage calculator does with a whole list of appliances at once.
One more thing worth knowing before you act on an annual figure: every watt this page counts also ends up in the room as heat. In heating season that is not waste at all, and it offsets part of what your heating system would otherwise have to replace — the quantity the heat loss calculator works out. In cooling season the same watt is charged twice, once at the appliance and again at the compressor that removes it. Neither effect is folded into the numbers above, because doing so would need a climate, a system efficiency and a season, and the moment a page starts assuming those it stops being arithmetic you can check. For the one load where the losses genuinely are inside the scope of the question, the ev charging cost calculator counts them explicitly, because there the gap between the meter and the battery is about a tenth of everything you buy.
Where the two appliance columns go
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.
The comparison is worked out in the page's own memory and never leaves it, so a survey of what a client is running and what it would cost to replace stays a conversation between you and them.