What It CostsHow We Calculate
Every calculator on this site is two steps: turn the appliance into kilowatt-hours, then turn kilowatt-hours into money at your price. What differs between tools is only how the first step is measured.
The formulas
- Steady draw: watts × hours ÷ 1,000 = kWh. Then × your price per kWh.
- Days a week: the daily figure × days ÷ 7, so a machine used at weekends is not counted as daily.
- A month is 30.44 days — a twelfth of a year, not 30. Twelve monthly figures therefore equal the yearly figure exactly, and the page never shows two numbers that disagree.
- Per cycle: kWh per cycle × cycles a week × 52 = kWh a year. Used for washing machines, dishwashers and tumble dryers, whose draw jumps between 100 W and 2,500 W during a programme — and for anything charged from a battery, where a “cycle” is one charge.
- Per use, in minutes: watts × minutes ÷ 60 ÷ 1,000 = kWh per use. Showers, air fryers, kettles and hair dryers run for minutes, so “hours a day” is the wrong question — the honest answer would be 0.13 and nobody thinks that way.
- By heated area: area in m² × watts per m² = the load. Electric underfloor heating is sold as output per square metre, and what a person knows is the size of the room, not the draw of the loop under it.
- Charging losses: battery figures include about 15% on top of the capacity in the cell, because that is what is lost as heat between the socket and the battery. It is the warmth you can feel in the plug, and leaving it out understates every charging figure.
- EV charging: energy into the battery = capacity × (target % − current %). Energy off the meter = that ÷ charging efficiency. Cost per mile = meter energy ÷ miles per kWh × price.
- Amps: watts ÷ volts. The same appliance draws half the amps at 240 V that it does at 120 V, while using exactly the same energy.
The one number we never supply
The price per kWh is always yours to type. Every tool pre-fills an approximate household average for the country you pick so the form is not empty, but nothing on this site depends on those figures being current. They differ by supplier, tariff, region and time of day, and a published average is out of date within months. The number on your bill is the only correct one.
Typical appliance figures
These are the presets. Each is a working figure with the usual range beside it — a rating plate on your own machine beats every one of them.
| Appliance | Working figure | Usual range |
|---|---|---|
| Window air conditioner | 900 W | 500–1,500 W |
| Central air conditioning | 3,500 W | 2,000–5,000 W |
| Electric space heater | 1,500 W | 750–2,000 W |
| Dehumidifier | 300 W | 200–700 W |
| Fridge freezer | 150 W running | 100–250 W |
| Electric kettle | 2,500 W | 2,000–3,000 W |
| Electric oven | 2,400 W | 2,000–3,000 W |
| Television, 55-inch LED | 90 W | 50–150 W |
| Gaming PC under load | 450 W | 300–800 W |
| Games console | 160 W | 50–220 W |
| Router, always on | 10 W | 5–20 W |
| Pool pump | 1,100 W | 700–2,000 W |
| Hot tub heater | 3,000 W | 1,500–6,000 W |
| Electric water heater | 4,000 W | 3,000–5,500 W |
| Pedestal or ceiling fan | 60 W | 20–100 W |
| Air purifier, auto | 30 W | 8–100 W |
| Electric shower | 9,500 W | 8,500–10,500 W |
| Air fryer | 1,500 W | 1,200–1,800 W |
| Electric underfloor heating | 150 W per m² | 100–200 W per m² |
And the per-cycle machines:
| Machine | kWh per cycle | Usual range |
|---|---|---|
| Washing machine, 30 °C | 0.7 | 0.4–1.4 |
| Washing machine, hot | 1.4 | 1.0–2.2 |
| Tumble dryer, vented | 3.3 | 2.5–4.5 |
| Tumble dryer, condenser | 2.5 | 2.0–3.5 |
| Tumble dryer, heat pump | 1.1 | 0.8–1.6 |
| Dishwasher, normal | 1.0 | 0.7–1.5 |
| Dishwasher, eco | 0.7 | 0.5–1.0 |
And the battery figures, per full charge including charging losses:
| Device | kWh per charge | Battery |
|---|---|---|
| Phone, 5,000 mAh | 0.022 | about 19 Wh |
| Tablet | 0.040 | 30–40 Wh |
| Laptop | 0.070 | 50–70 Wh |
| Power bank, 20,000 mAh | 0.085 | about 74 Wh |
| E-bike | 0.575 | 400–750 Wh |
Running hours, not hours plugged in
The commonest mistake in this whole subject. A fridge draws its 150 W for roughly a third of the day, not all of it. A thermostatically controlled heater in a room that has reached temperature may run half the time. Enter the hours the appliance is actually working; a plug-in energy monitor settles it for the price of a takeaway.
Where the figures come from
Typical wattages and per-cycle energy follow published US Department of Energy and ENERGY STAR data. Electricity price references, used only as pre-filled defaults, come from the US Energy Information Administration and Eurostat. The AC home charging loss of 8–15% is the documented range for onboard chargers and battery thermal management; 10% is used as the default. Everything runs in your browser — nothing is stored, and nothing is sent anywhere.