The wattage on the label is four different things

Every page about appliance electricity does the same arithmetic: take the watts, multiply by hours, multiply by the tariff. It is a reasonable-looking calculation and it is wrong for most of the appliances people ask about.

Not slightly wrong. On a refrigerator it overstates by several times. On an iron it produces a ceiling and presents it as an estimate. On a kettle it answers a question nobody asked, because the wattage does not affect the cost at all.

The reason is that "watts" is not one measurement. It is four, and which one you are holding depends on the appliance.

1. A measured draw — televisions and monitors

This is the case people assume they always have. Certification programmes test televisions under a defined procedure and publish the power drawn while the set is on. It is a real measurement of a real model, and it can be multiplied by hours.

One trap remains even here, and it caught us before we published anything. The same dataset carries two power fields: the certification ceiling and the measured draw. They differ by about 25% — 147.81 W against 117.69 W on the same model. The first is the maximum a set may draw and still qualify; the second is what it actually drew on the bench. Quoting the ceiling as consumption inflates every downstream figure, and it is the field with the more official-sounding name.

2. A cycled draw — refrigerators, washing machines, dishwashers

A compressor does not run continuously. It runs in cycles, sized to the room, the door openings and the thermostat. So the current it draws while running is a real number that describes a state the appliance is in for a fraction of the day.

Multiply it by 24 and you get a figure several times the truth. This is the single most common error in the category, and it is why fridge estimates online disagree so violently.

What actually exists for these appliances is a certified annual consumption in kilowatt-hours, measured over a test cycle. That is the honest unit, and there is no published wattage to convert it into. On this site those devices carry a yearly figure and no watts at all — not because we could not find the watts, but because a constant wattage for them does not exist.

3. A ceiling, not an average — irons, and anything with a thermostat

An iron is rated 1200 to 1700 watts. That rating describes the heating element while it is switched on, and a thermostat switches it on and off throughout the session.

So the nameplate is an upper bound. The average draw across half an hour of ironing is lower — and by how much, nobody publishes. There is no certification programme for irons and no US test procedure for them at all.

This puts us in an awkward position that is worth stating plainly rather than papering over: we can give you a ceiling and the arithmetic, and we can tell you the ceiling is high. We cannot give you a measured average, because none exists. Every site that prints one has estimated it and not told you.

The same applies, in the same direction, to microwave standby: the clock and display draw continuously and can exceed the cooking itself over a year, and nobody certifies that figure either.

4. Irrelevant — kettles, and anything that heats a fixed quantity

Here the wattage genuinely does not matter, and this is the most useful thing on this page.

Heating one litre of water from room temperature to boiling takes 4,186 joules per kilogram per degree, times one kilogram, times eighty degrees — 334,880 joules, or 0.093 kWh. That figure contains no wattage. It is the same whether the energy arrives in two minutes or six.

A US kettle is capped near 1500 W because a 120 V socket on a 15 A circuit leaves 1800 W for the whole branch. A UK kettle on 230 V is commonly 3000 W. The British kettle boils in half the time for the same electricity. The transatlantic complaint is true and costs nothing.

What does change the cost is how much water you put in. Boiling a full 1.7-litre kettle for one mug costs about six times what the mug needed — a far larger effect than any difference between models, and the only lever that is actually yours.

Why this matters beyond trivia

Take the toaster and the refrigerator, both real figures from this site:

The toaster draws twenty-four times more and costs fifteen times less. Everything in that gap is duration — four minutes a day against every hour of the year.

Which is the general lesson: a wattage without a duration is not an answer, and for half of these appliances the wattage is not even the right input. The appliances people worry about are usually not the ones costing them money, and the reason is that they are comparing the wrong number.

What to do with a figure you find elsewhere

• Ask which of the four it is. Measured draw, cycled draw, nameplate ceiling, or irrelevant. If the page does not say, it does not know.
• If the appliance has a compressor or a thermostat, refuse the multiplication. Watts × hours does not apply to a duty cycle.
• If a page gives a single "per day" figure, find out whether it means 24 hours or the hours you actually use it. The difference is six-fold, and half the pages in this category never say which they mean.
• Check whether the number is a ceiling with an official-sounding name. Certification maximums and power-supply ratings are both larger than the truth, and both are printed more prominently than the measurement.